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Red Hat Enterprise Linux 5.6 was released last week (January 2011), nearly ten months since the release of 5.5 in March 2010. So let's use this opportunity to take a quick look back over the vulnerabilities and security updates made in that time, specifically for Red Hat Enterprise Linux 5 Server.

Errata count

The chart below illustrates the total number of security updates issued for Red Hat Enterprise Linux 5 Server if you had installed 5.5, up to and including the 5.6 release, broken down by severity. It's split into two columns, one for the packages you'd get if you did a default install, and the other if you installed every single package (which is unlikely as it would involve a bit of manual effort to select every one). For a given installation, the number of package updates and vulnerabilities that affected you will depend on exactly what you have installed or removed.

Number of security errata between
     5.5 and 5.6

So, for a default install, from release of 5.5 up to and including 5.6, we shipped 57 advisories to address 206 vulnerabilities. 10 advisories were rated critical, 27 were important, and the remaining 20 were moderate and low.

Or, for all packages, from release of 5.5 to and including 5.6, we shipped 80 advisories to address 300 vulnerabilities. 12 advisories were rated critical, 34 were important, and the remaining 34 were moderate and low.

Critical vulnerabilities

The 12 critical advisories addressed 49 critical vulnerabilities across just 3 different packages:

  1. An update to the Exim Internet Mailer, (December 2010), where an unauthenticated remote attacker could run arbitrary code as root on a server. Exim is not a default package or enabled by default. There is a public exploit for this issue which worked on Red Hat Enterprise Linux 5.
  2. Two updates over three advisories to Samba, (June 2010 for Samba 3.0 and Samba 3.3, September 2010 for Samba 3.0 and Samba 3.3), where a malicious client could send a specially-crafted SMB packet to the Samba server, potentially resulting in arbitrary code execution with the privileges of the Samba server. I'm not aware of any working public exploits for these issues.
  3. Eight updates to Firefox (March 2010, June 2010, 20 July 2010, 23 July 2010, September 2010, 19 October 2010, 27 October 2010, December 2010) where a malicious web site could potentially run arbitrary code as the user running Firefox.

Updates to correct 48 out of the 49 critical vulnerabilities were available via Red Hat Network either the same day or the next calendar day after the issues were public. The update to fix Exim took 3 calendar days from the date of the report to the Exim developers.

Overall, for Red Hat Enterprise Linux 5 since release until 5.6, 97% of critical vulnerabilities have had an update available to address them available from the Red Hat Network either the same day or the next calendar day after the issue was public.

Other significant vulnerabilities

Although not in the definition of critical severity, also of interest during this period were several kernel flaws that where an local user could gain root privileges. The following had publicly available exploits:

Previous updates

To compare these statistics with previous update releases we need to take into account that the time between each update is different. So looking at a default installation and calculating the number of advisories per month gives the following chart:

Errata per month for each update release

This data is interesting to get a feel for the risk of running Enterprise Linux 5 Server, but isn't really useful for comparisons with other major versions, distributions, or operating systems -- for example, a default install of Red Hat Enterprise Linux 4AS did not include Firefox, but 5 Server does. You can use our public security measurement data and tools, and run your own custom metrics for any given Red Hat product, package set, timescales, and severity range of interest.

See also: 5.4 to 5.5, 5.3 to 5.4, 5.2 to 5.3, 5.1 to 5.2, and 5.0 to 5.1 risk reports.


You have a new email! (ping!)

Hold on a second. It might be important. I'd better go and read it. Oh it's just a note confirming some meeting for next week. Deleted. Now, what was I working on?

A few years ago, when I was analysing where my time was going, (and why I was working 60+ hour weeks), I figured out that the context switching caused by being unable to concentrate on a task for more than a few minutes was a major productivity drain.

It's hard to resist a new email. My new cellphone takes great delight in having 'push' email and would really like to beep on each new message I receive. The web is full of gmail notifier applications designed specifically to interrupt you to some important new mail. Even my favourite command-line email client, Alpine, likes to ping you about new mail arriving in your inbox even if you're busy in some other mailbox or composing a mail.

Alpine ought to have some sort of "don't notify me" option, but in the meantime I apply the brute-force patch below to disable it.

This 5-minute patch has saved me several hours of task switching every week, and although this means it can sometimes be an hour or two between me checking my inbox, no one has really noticed.

--- alpine-2.00/pith/newmail.c.orig	2010-07-19 16:47:01.127480500 +0100
+++ alpine-2.00/pith/newmail.c	2010-07-19 16:47:35.657602347 +0100
@@ -680,7 +680,7 @@
     }
 
     format_new_mail_msg(folder, number, e, intro, from, subject, subjtext, sizeof(subject));
-
+#if 0
     if(!for_new_mail_win)
       q_status_message5(SM_ASYNC | SM_DING, 0, 60,
 		      "%s%s%s%.80s%.80s", intro,
@@ -706,6 +706,7 @@
 #endif
     }
 #endif
+#endif
 
     if(pith_opt_icon_text){
 	if(F_ON(F_ENABLE_XTERM_NEWMAIL, ps_global)


Two years ago I published a table of Vulnerability and threat mitigation features in Red Hat Enterprise Linux and Fedora. Now that we've released Red Hat Enterprise Linux 6, it's time to update the table. Thanks to Eugene Teo for collating this information.

Between releases there are lots of changes made to improve security and we've not listed everything; just a high-level overview of the things we think are most interesting that help mitigate security risk. We could go into much more detail, breaking out the number of daemons covered by the SELinux default policy, the number of binaries compiled PIE, and so on.

Note that this table is for the most common architectures, x86 and x86_64 only; other supported architectures may vary.

Features Red Hat Enterprise Linux
3456
2003 Oct2005 Feb2007 Mar2010 Nov
Firewall by default YY YY
Signed updates required by default YY YY
NX emulation using segment limits by default Y(since 9/2004)Y Y Y
Support for Position Independent Executables (PIE) Y(since 9/2004)YYY
Address Randomization (ASLR) for Stack/mmap by default Y (since 9/2004)YYY
ASLR for vDSO (if vDSO enabled) no vDSOYYY
Support for NULL pointer dereference protection Y(since 11/2009) Y(since 9/2009) Y(since 5/2008) Y
NX for supported processors/kernels by default Y(since 9/2004)YYY
Support for block module loading via cap-bound sysctl tunable
or /proc/sys/kernel/cap-bound
YY Y no cap-bound
Restricted access to kernel memory by default  YYY
Support for SELinux  YYY
SELinux enabled with targeted policy by default  YYY
glibc heap/memory checks by default  YYY
Support for FORTIFY_SOURCE, used on selected packages  YYY
Support for ELF Data Hardening  YYY
All packages compiled using FORTIFY_SOURCE   YY
All packages compiled with stack smashing protection   YY
SELinux Executable Memory Protection   YY
glibc pointer encryption by default   YY
Enabled NULL pointer dereference protection by default     Y(since 5/2008) Y
Enabled write-protection for kernel read-only data structures
by default
    Y Y
FORTIFY_SOURCE extensions including C++ coverage    Y
Support for block module loading via modules_disabled
sysctl tunable or /proc/sys/kernel/modules_disabled
      Y
Support for SELinux to restrict the loading of kernel modules
by unprivileged processes in confined domains
      Y
Enabled kernel -fstack-protector buffer overflow detection by default       Y
Support for sVirt labelling to provide security over guest instances
      Y
Support for SELinux to confine users' access on a system
      Y
Support for SELinux to test untrusted content via a sandbox
      Y
Support for SELinux X Access Control Extension (XACE)
      Y


It came as no surprise when Microsoft admitted to quiet security patching. We knew many years ago that they did this: not counting extra vulnerabilities that were found internally or by researchers contracted to work for them. For closed source, single vendor software, this isn't too big of a deal - it's not like the user has a choice if they need to update some application to address one critical vulnerability or 20.

When you look back, before they admitted to this practice, Microsoft actively used vulnerability counts in reports as a tool to discredit the security of open source distributions. Famously even Steve Ballmer participated in counting vulnerabilities using candy.

In other news, the Red Hat Enterprise Linux 4 risk report we release each year has been published (PDF). This whitepaper looks at the state of security for the first five years of Red Hat Enterprise Linux 4 from its release on February 15th, 2005. It includes metrics, key vulnerabilities, and the most common ways users were affected by security issues.

"Red Hat knew about 52% of the security vulnerabilities that we fixed in advance of them being publicly disclosed. The average time between Red Hat knowing about an issue and it being made public was 22 days (median 10 days).... A default installation of Red Hat Enterprise Linux 4 AS was vulnerable to 14 critical security issues over the entire five years. "


Red Hat Enterprise Linux 5.5 was released at the end of March 2010, just under 7 months since the release of 5.4 in September 2009. So let's use this opportunity to take a quick look back over the vulnerabilities and security updates we've made in that time, specifically for Red Hat Enterprise Linux 5 Server.

Errata count

The chart below illustrates the total number of security updates issued for Red Hat Enterprise Linux 5 Server if you had installed 5.4, up to and including the 5.5 release, broken down by severity. I've split it into two columns, one for the packages you'd get if you did a default install, and the other if you installed every single package (which is unlikely as it would involve a bit of manual effort to select every one). For a given installation, the number of package updates and vulnerabilities that affected you will depend on exactly what you have installed or removed.

missing graph

So for a default install, from release of 5.4 up to and including 5.5, we shipped 52 advisories to address 140 vulnerabilities. 5 advisories were rated critical, 14 were important, and the remaining 33 were moderate and low.

Or, for all packages, from release of 5.4 to and including 5.5, we shipped 75 advisories to address 187 vulnerabilities. 6 advisories were rated critical, 18 were important, and the remaining 51 were moderate and low.

Critical vulnerabilities

The 6 critical advisories were for 3 different packages. Given the nature of the flaws, ExecShield protections in RHEL5 should make exploiting the memory flaws harder.

  1. Four updates to Firefox (September 2009, October 2009, December 2009, February 2010) where a malicious web site could potentially run arbitrary code as the user running Firefox.
  2. An update to kdelibs (November 2009), where a malicious web site could potentially run arbitrary code as the user running the Konqueror browser. kdelibs is not a default installation package.
  3. An update to krb5, the Kerberos network authentication system (January 2010), where a remote KDC client could cause a crash or run arbitrary code as root. This issue only affected users that have configured and enabled krb5.

Updates to correct 24 out of the 25 critical vulnerabilities were available via Red Hat Network either the same day, or up to one calendar day after the issues were public. The update to fix Konqueror took us 4 calendar days.

Overall, for Red Hat Enterprise Linux 5 since release to date, 98% of critical vulnerabilities have had an update available to address them available from the Red Hat Network either the same day or the next calendar day after the issue was public.

Other significant vulnerabilities

Red Hat Enterprise Linux since 5.2 contained backported patches from the upstream Linux kernel to add the ability to restrict unprivileged mapping of low memory, designed to mitigate NULL pointer dereference flaws. In the last risk report we mentioned it was found that this protection was not sufficient, as a system with SELinux enabled was more permissive in allowing local users in the unconfined_t domain to map low memory areas even if the mmap_min_addr restriction is enabled. This is CVE-2009-2695 and was addressed in a kernel update in November 2009.

Previous updates

To compare these statistics with previous update releases we need to take into account that the time between each update is different. So looking at a default installation and calculating the number of advisories per month gives the results illustrated by the following chart:

missing graph

This data is interesting to get a feel for the risk of running Enterprise Linux 5 Server, but isn't really useful for comparisons with other versions, distributions, or operating systems -- for example, a default install of Red Hat Enterprise Linux 4AS did not include Firefox, but 5 Server does. You can use our public security measurement data and tools, and run your own custom metrics for any given Red Hat product, package set, timescales, and severity range of interest.

See also: 5.3 to 5.4, 5.2 to 5.3, 5.1 to 5.2, and 5.0 to 5.1 risk reports.


The 2010 CWE/SANS Top 25 Most Dangerous Programming Errors was published today listing the most widespread issues that lead to software vulnerabilities.

During the creation and review of the list we spent some time to see how closely last years list matched the types of flaws we deal with at Red Hat. We first looked at all the issues that Red Hat fixed across our entire product portfolio in the 2009 calendar year and filtered out those that had the highest severity. All our 2009 vulnerabilities have CVSS scores, so we filtered on those that have a CVSS base score of 7.0 or above[1].

There were 22 vulnerabilities that matched, and we mapped each one to the most appropriate CWE. This gives us 11 flaw types which led to the most severe flaws affecting Red Hat in 2009:

CWECWE DescriptionCWE/SANS
top 25?
Number of
Vulnerabilities
CWE-476NULL Pointer DereferenceNo (on cusp)6
CWE-120Buffer Copy without Checking Size of InputYes3
CWE-129Improper Validation of Array Index Yes3
CWE-131Incorrect Calculation of Buffer Size Yes3
CWE-78OS Command InjectionYes1
CWE-285Improper Access Control (Authorization)Yes1
CWE-362Race ConditionYes1
CWE-330 Use of Insufficiently Random Values No (on cusp)1
CWE-590Free of Memory not on the HeapNo1
CWE-672Use of a Resource after Expiration or ReleaseNo (on cusp)1
CWE-772Missing Release of Resource after Effective LifetimeNo (on cusp)1

10 of the 11 CWE are mentioned in the 2010 CWE/SANS document, although 4 of them are on "the cusp" and didn't make it into the top 25.

This quick review shows us that 2009 was the year of the kernel NULL pointer dereference flaw, as they could allow local untrusted users to gain privileges, and several public exploits to do just that were released. For Red Hat, interactions with SELinux prevented them being able to be easily mitigated, until the end of the year when we provided updates. Now, in 2010, the upstream Linux kernel and many vendors ship with protections to prevent kernel NULL pointers leading to privilege escalation. So although 2009 was the year where CWE-476 mattered to Linux administrators, it didn't make the SANS/CWE top 25 as this flaw type should not lead to severe issues (as long as the protections remain sufficient).

Here is a breakdown with the complete data set to show the CVSS scores and packages affected:

CVECWEtop 25?CVSS
base
Fixed in
CVE-2008-5182 CWE-362Yes 7.2Red Hat Enterprise Linux 5 (kernel)
CVE-2009-0065 CWE-129Yes 8.3Red Hat Enterprise Linux 4,5,MRG (kernel)
CVE-2009-0692 CWE-120Yes 8.3Red Hat Enterprise Linux 3,4 (dhcp)
CVE-2009-0778 CWE-772No (on cusp) 7.1Red Hat Enterprise Linux 5 (kernel)
CVE-2009-0846 CWE-590No 9.3Red Hat Enterprise Linux 2.1, 3 (krb5) [2]
CVE-2009-1185 CWE-131Yes 7.2Red Hat Enterprise Linux 5 (udev)
CVE-2009-1385 CWE-129Yes 7.1Red Hat Enterprise Linux 3,4,5,MRG (kernel)
CVE-2009-1439 CWE-131Yes 7.1Red Hat Enterprise Linux 4,5,MRG (kernel)
CVE-2009-1579 CWE-78Yes 7.5Red Hat Enterprise Linux 3,4,5 (squirrelmail)
CVE-2009-1633 CWE-131Yes 7.1Red Hat Enterprise Linux 4,5,MRG (kernel)
CVE-2009-2406 CWE-120Yes 7.2Red Hat Enterprise Linux 5 (kernel)
CVE-2009-2407 CWE-120Yes 7.2Red Hat Enterprise Linux 5 (kernel)
CVE-2009-2692 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 3,4,5,MRG (kernel)
CVE-2009-2694 CWE-129Yes 7.5Red Hat Enterprise Linux 3,4,5 (pidgin)
CVE-2009-2698 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 3,4,5 (kernel)
CVE-2009-2848 CWE-672No (on cusp) 7.2Red Hat Enterprise Linux 3,4,5,MRG (kernel)
CVE-2009-2908 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 5 (kernel)
CVE-2009-3238 CWE-330No (on cusp) 7.8Red Hat Enterprise Linux 4,5,MRG (kernel)
CVE-2009-3290 CWE-285Yes 7.2Red Hat Enterprise Linux 5 (kvm)
CVE-2009-3547 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 3,4,5,MRG (kernel)
CVE-2009-3620 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 4,5,MRG (kernel)
CVE-2009-3726 CWE-476No (on cusp) 7.2Red Hat Enterprise Linux 5,MRG (kernel)

[1] NIST NVD rate vulnerabilities as "High" severity if they have a CVSS base score of 7.0-10.0. This ends up excluding flaws in web browsers such as Firefox which can have a maximum CVSS base score of 6.8.

[2] Red Hat Enterprise Linux 4 and 5 were also affected by this vulnerability, but with a lower CVSS base score of 4.3, due to the extra runtime pointer checking.


Red Hat Enterprise Linux 5.4 was released today, just over 7 months since the release of 5.3 in January 2009. So let's use this opportunity to take a quick look back over the vulnerabilities and security updates we've made in that time, specifically for Red Hat Enterprise Linux 5 Server.

Errata count

The chart below illustrates the total number of security updates issued for Red Hat Enterprise Linux 5 Server as if you installed 5.3, up to and including the 5.4 release, broken down by severity. I've split it into two columns, one for the packages you'd get if you did a default install, and the other if you installed every single package (which is unlikely as it would involve a bit of manual effort to select every one). For a given installation, the number of package updates and vulnerabilities that affected you will depend on exactly what you have installed or removed.

missing graph

So for a default install, from release of 5.3 up to and including 5.4, we shipped 51 advisories to address 166 vulnerabilities. 8 advisories were rated critical, 18 were important, and the remaining 25 were moderate and low.

Or, for all packages, from release of 5.3 to and including 5.4, we shipped 78 advisories to address 251 vulnerabilities. 9 advisories were rated critical, 28 were important, and the remaining 41 were moderate and low.

Critical vulnerabilities

The 9 critical advisories were for just 3 different packages. In all the cases below, given the nature of the flaws, ExecShield protections in RHEL5 should make exploiting these memory flaws harder.

  1. Seven updates to Firefox (February, March 4th, March 27th, April 21st, April 27th, June, July ) where a malicious web site could potentially run arbitrary code as the user running Firefox.
  2. An update to kdelibs (June), where a malicious web site could potentially run arbitrary code as the user running the Konqueror browser. kdelibs is not a default installation package.
  3. An update to the NSS library (July), where a service could present a malicious SSL certificate causing a heap overflow which could potentially run arbitrary code as the user running a browser such as Firefox.

Updates to correct all of these critical vulnerabilities were available via Red Hat Network either the same day, or up to one calendar day after the issues were public.

In fact for Red Hat Enterprise Linux 5 since release and to date, every critical vulnerability has had an update available to address it available from the Red Hat Network either the same day or the next calendar day after the issue was public.

Other significant vulnerabilities

Although not in the definition of critical severity, also of interest during this period were several NULL pointer dereference kernel issues. NULL pointer dereference flaws in the Linux kernel can often be easily abused by a local unprivileged user to gain root privileges through the mapping of low memory pages and crafting them to contain valid malicious instructions:

Red Hat Enterprise Linux since 5.2 has contained backported patches from the upstream Linux kernel to add the ability to restrict unprivileged mapping of low memory, designed to mitigate NULL pointer dereference flaws. However it was found that this protection was not sufficient, as a system with SELinux enabled is more permissive in allowing local users in the unconfined_t domain to map low memory areas even if the mmap_min_addr restriction is enabled. This is CVE-2009-2695 and will be addressed in a future kernel update.

Mitigations

Red Hat Enterprise Linux 5 shipped with a number of security technologies designed to make it harder to exploit vulnerabilities and in some cases block exploits for certain flaw types completely. From 5.3 to 5.4 there were three flaws blocked that would otherwise have required critical updates:

Previous updates

To compare these statistics with previous update releases we need to take into account that the time between each update is different. So looking at a default installation and calculating the number of advisories per month gives the results illustrated by the following chart:

missing graph

This data is interesting to get a feel for the risk of running Enterprise Linux 5 Server, but isn't really useful for comparisons with other versions, distributions, or operating systems -- for example, a default install of Red Hat Enterprise Linux 4AS did not include Firefox, but 5 Server does. You can use our public security measurement data and tools, and run your own custom metrics for any given Red Hat product, package set, timescales, and severity range of interest.

See also: 5.2 to 5.3, 5.1 to 5.2, and 5.0 to 5.1 risk reports.


Red Hat Enterprise Linux 5.3 was released today, around 8 months since the release of 5.2 in May 2008. So let's use this opportunity to take a quick look back over the vulnerabilities and security updates we've made in that time, specifically for Red Hat Enterprise Linux 5 Server.

The chart below shows the total number of security updates issued for Red Hat Enterprise Linux 5 Server as if you installed 5.2, up to and including the 5.3 release, broken down by severity. I've split it into two columns, one for the packages you'd get if you did a default install, and the other if you installed every single package (which is unlikely as it would involve a bit of manual effort to select every one). So, for a given installation, the number of packages and vulnerabilities will probably be somewhere between the two.

missing graph

So for a default install, from release of 5.2 up to and including 5.3, we shipped 45 advisories to address 127 vulnerabilities. 7 advisories were rated critical, 21 were important, and the remaining 17 were moderate and low.

For all packages, from release of 5.2 to and including 5.3, we shipped 61 advisories to address 181 vulnerabilities. 7 advisories were rated critical, 28 were important, and the remaining 26 were moderate and low.

The 7 critical advisories were for just 3 different packages:

  1. Five updates to Firefox (July, July, September, November, December) where a malicious web site could potentially run arbitrary code as the user running Firefox. Given the nature of the flaws, ExecShield protections in RHEL5 should make exploiting these memory flaws harder.
  2. An update to Samba (May), where a remote attacker who can connect and send a print request to a Samba server could cause a heap overflow. The Red Hat Security Response Team believes it would be hard to remotely exploit this issue to execute arbitrary code due to the default enabled SELinux targeted policy and the default enabled SELinux memory protection tests. We are not aware of any public exploit for this issue.
  3. An update to OpenSSH (August), provided to mitigate an intrusion into certain Red Hat computer systems. The attacker was able to sign a small number of tampered packages but they were not distributed on the Red Hat Network. We classified this update as critical to ensure any tampered packages would be replaced with official packages.

Although not of critical severity, also of interest during this period were the spoofing attacks on DNS servers. We provided an update to BIND (July) adding source port randomization to help mitigate these attacks.

Updates to correct all of these critical vulnerabilities (as well as migitate the BIND issue) were available via Red Hat Network either the same day, or one calendar day after the issues were public.

In fact for Red Hat Enterprise Linux 5 since release and to date, every critical vulnerability has had an update available to address it available from the Red Hat Network either the same day or the next calendar day after the issue was public.

To compare this with the last updates we need to take into account that the time between each update is different. So looking at a default installation and calculating the number of advisories per month gives the following chart:

missing graph

Red Hat Enterprise Linux 5 shipped with a number of security technologies designed to make it harder to exploit vulnerabilities and in some cases block exploits for certain flaw types completely. For 5.2 to 5.3 there were two flaws blocked that would otherwise have required updates:

  1. A double-free flaw in unzip. The glibc pointer checking limited the exploitability of this issue to just a crash of unzip, a client application, which does not have security implications. No security update was needed.
  2. Two format string flaws in c++filt. The format string protection caused these issues to have no security implications. No security update was needed.

This data is interesting to get a feel for the risk of running Enterprise Linux 5 Server, but isn't really useful for comparisons with other versions, distributions, or operating systems -- for example, a default install of Red Hat Enterprise Linux 4AS did not include Firefox, but 5 Server does. You can use our public security measurement data and tools, and run your own custom metrics for any given Red Hat product, package set, timescales, and severity range of interest.

See also:5.1 to 5.2 risk report


Red Hat Enterprise Linux 5.2 was released last week, around 6 months since the release of 5.1 in November 2007. So let's use this opportunity to take a quick look back over the vulnerabilities and security updates we've made in that time, specifically for Red Hat Enterprise Linux 5 Server.

The graph below shows the total number of security updates issued for Red Hat Enterprise Linux 5 Server starting at 5.1 up to and including the 5.2 release, broken down by severity. I've split it into two columns, one for the packages you'd get if you did a default install, and the other if you installed every single package (which is unlikely as it would involve a bit of manual effort to select every one). So, for a given installation, the number of packages and vulnerabilities will probably be somewhere between the two.

missing graph

So for a default install, from release of 5.1 up to and including 5.2, we shipped 46 updates to address 119 vulnerabilities. 8 advisories were rated critical, 24 were important, and the remaining 14 were moderate and low.

For all packages, from release of 5.1 to and including 5.2, we shipped 62 updates to address 179 vulnerabilities. 9 advisories were rated critical, 29 were important, and the remaining 24 were moderate and low.

The nine critical updates were in five different packages:

  1. Four updates to Firefox (November, February, March, April) where a malicious web site could potentially run arbitrary code as the user running Firefox. Given the nature of the flaws, ExecShield protections in RHEL5 should make exploiting these memory flaws harder.
  2. An update to the GnuTLS library (May), where a remote attacker who can connect to a server making use of GnuTLS could cause a buffer overflow. In Red Hat Enterprise Linux 5, the CUPS print server uses GnuTLS.

  3. An update to MIT Kerberos (March), where a remote attacker who can conect to the krb5kdc or kadmind services could cause a buffer overflow.

  4. An update to OpenPegasus (January), where a remote attacker who can connect to OpenPegasus could cause a buffer overflow. The Red Hat Security Response Team believes that it would be hard to remotely exploit this issue to execute arbitrary code, due to the default SELinux targeted policy, and the default SELinux memory protection tests.

  5. Two updates to Samba (November, December) where a remote attacker who can connect to the Samba port could cause buffer overflows. In addition to ExecShield making this harder to exploit, the impact of any sucessful exploit would be reduced as Samba is constrained by an SELinux targeted policy (enabled by default).

Updates to correct all of these critical issues were available via Red Hat Network either the same day, or one calendar day after the issues were public.

To get a better idea of risk we need to look not only at the vulnerabilities but also the exploits written for those vulnerabilities. A proof of concept exploit exists publicly for one of the Samba flaws, CVE-2007-6015, but we are not aware of public exploits for any other of those critical vulnerabilities. Also of high risk was an important "zero-day" exploit affecting the Linux kernel where a local unprivileged user could gain root privileges. Red Hat Enterprise Linux 5.1 was affected and a fix was available two calendar days after public disclosure.

Red Hat Enterprise Linux 5 shipped with a number of security technologies designed to make it harder to exploit vulnerabilities and in some cases block exploits for certain flaw types completely. For the period of this study there were two flaws blocked that would otherwise have required updates:

  1. A double-free flaw in CUPS. The glibc pointer checking limited the exploitability of this issue to just a crash of CUPS and not the ability to execute arbitrary code. code execution. We still issued an update, as a remote attacker could trigger this flaw and cause CUPS to crash.
  2. An uninitialized pointer free flaw in unzip, caught by the glibc pointer checking. As exploitation of this flaw results in just a crash of a user application, no updates were needed.

This data is interesting to get a feel for the risk of running Enterprise Linux 5 Server, but isn't really useful for comparisons with other versions or distributions -- for example, a default install of Red Hat Enterprise 4AS did not include Firefox. You can get the results I presented above for yourself by using our public security measurement data and tools, and run your own custom metrics for any given Red Hat product, package set, timescales, and severities.

See also 5.0 to 5.1 risk report


It sometimes seems like the Security Response Team at Red Hat are pushing security updates every day, but actually a default installation of Enterprise Linux 4 AS was vulnerable to only 7 critical security issues in the first three years since release. But to get a picture of the risk you need to do more than count vulnerabilities.

My full risk report was published yesterday in Red Hat Magazine and reveals the state of security since the release of Red Hat Enterprise Linux 4 including metrics, key vulnerabilities, and the most common ways users were affected by security issues.

"Red Hat knew about 49% of the security vulnerabilities that we fixed in advance of them being publicly disclosed. For those issues, the average notice was 21 calendar days, although the median was much lower, with half the private issues having advance notice of 8 days or less."

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Hi! I'm Mark Cox. This blog gives my thoughts and opinions on my security work, open source, fedora, home automation, and other topics.