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mark :: blog :: red hat
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.
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:
- 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.
- 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.
- An update to MIT Kerberos (March),
where a remote attacker who can conect to the krb5kdc or kadmind
services could cause a buffer overflow.
- 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.
- 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:
- 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.
- 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."
Last Friday, just as I was finishing work for the day, an email
appeared in my mailbox from the UK CPNI announcing a public remote
code execution flaw in Apache on HP-UX. As Chair of the Apache
Software Foundation Security Team I knew there were no outstanding remote code
execution flaws in Apache HTTP server (in fact we've not had a remote
code execution flaw for many years) so I was expecting to invoke the
Red Hat Critical Action Plan which would have meant a rather long
weekend for me, my team, and various development and quality engineering staff.
First thing to do was to find the original source of the advisory,
as co-ordination centres and research firms are known to often play the
Telephone game, with advisory texts mangled beyond recognition. Following
the links led to the actual
advisory on the HP site. This describes the vulnerability as follows:

But then they give the CVE name for the flaw, CVE-2007-6388,
which is a known public flaw fixed last month in various
Apache versions from the ASF and in updates from various vendors
that ship Apache (including Red Hat).
This flaw is a cross-site scripting flaw in the mod_status module.
Note that the server-status page is not enabled by default and it is
best practice to not make this publicly available.
I wrote mod_status over 12 years ago and so I know that this flaw is exactly
how the ASF describes it; it definitely can't let a remote attacker execute
arbitrary code on your Apache HTTP server, under any circumstances.
I fired off a quick email to a couple of contacts in the HP security
team and they confirmed that the flaw they fixed is just the cross-site
scripting flaw, not a remote code flaw. The CVSS ratings they give in
their advisory are consistent with it being a cross-site scripting flaw
too.
So happy with a false alarm we cancelled our Critical Action Plan and
I went off and had a nice weekend
practicing
taking panoramas without a tripod ready for an upcoming holiday. My first
attempt came out better than I expected:

Secunia released a security summary report for 2007 and surprisingly
gave a count for Red Hat for the year at over 600 vulnerabilities. I
had no idea how they got to this number, it certainly doesn't match
our own publicly available metrics at
http://www.redhat.com/security/data/metrics
Using our public tool, for every Red Hat product and service, for 2007
we issued 306 advisories to fix 404 vulnerabilities. Of those 404
vulnerabilities 41 were critical (on the scale used by Microsoft and
Red Hat).
Most people are not going to be using every Red Hat product, so taking
just Enterprise Linux product you find 348 vulnerabilities, of which 27
were critical. A given user is going to only be vulnerable to the issues that affect
the products and packages they have installed. Using the scripts on
our pages you can figure it out for your own circumstances. But as an
example, the default installation of Red Hat Enterprise Linux 4 AS had
172 vulnerabilities of which 4 were critical.
The Secunia report does actually make it clear you can't use their
vulnerability count as a method of comparing platforms, in part due to the
differences in methodology of the vendors, but I'm sure this won't stop
some press from jumping to conclusions if they don't read the actual report.
I've asked Secunia how they got to their number of vulnerabilities, but in the
meantime, a raw count of vulnerabilities is only a small part of the
overall risk exposure in using a product. I've got some more reports that go
into this in more detail for two years of Enterprise Linux 4 and Enterprise Linux
5.0 to 5.1.
Update: Coverage of this: ZDNet
Update: Secunia told me that they treat each advisory separately; so for example
yesterday we issued updates for some moderate severity issues in
the Apache Web server, but we did separate advisories for each affected
product: Red Hat Enterprise Linux 2.1, 3, 4, 5, Red Hat Application Stack v1, v2.
So in this case the same Apache vulnerability would be counted 6 times.
A year ago I published a table of
Security Features in
Red Hat Enterprise Linux and Fedora Core. Since then we've released
two more Fedora versions, and a Red Hat Enterprise Linux, so it's time to
update the table.
Between releases there are lots of changes made to improve security and I've not
listed everything; just a high-level overview of the things I 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.
1 Since June 2004, 2 Since September 2004, 3 Selected Architectures
Late last month I spent a day with the Red Hat Magazine team talking
about vulnerability response. The first video
is now available and talks about the role of Red Hat in dealing
with vulnerabilities in third party software. The video was shot in
my home office which explains the calming green paint; it's hard to
get too stressed in a pale green room.
Red Hat Enterprise Linux 5.1 was released today, around 8 months since the
release of 5.0 in March 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 up to and including the 5.1 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 be somewhere between the two extremes.
So for all packages, from release up to and including 5.1, we shipped 94 updates
to address 218 vulnerabilities. 7 advisories were rated critical, 36 were
important, and the remaining 51 were moderate and low.
For a default install, from release up to and including 5.1, we shipped 60
updates to address 135 vulnerabilities. 7 advisories were rated critical, 26
were important, and the remaining 27 were moderate and low.
- These figures include ten updates we released on the day we shipped 5.0. This was
because we froze package updates some months before releasing the product. Only
one of those updates was rated critical, an update to Firefox.
- The six other critical updates were:
- Three more updates to Firefox (May, July, October)
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.
- An update to the Kerberos telnet deamon (April)
A remote attacker who can access the telnet
port of a target machine could log in as root without requiring a
password. None of the standard protection mechanisms help prevent
exploitation of this issue, however the krb5 telnet daemon is not
enabled by default in Enterprise Linux 5 and the default firewall rules
block remote access to the telnet port. This flaw did not affect the
more common telnet daemon distributed in the telnet-server
package.
- An update to Samba (May) where
a remote attacker could cause a heap overflow. 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).
- An update to the PCRE library (November). This
was labelled critical because the Konqueror web browser uses PCRE to handle
regular expressions in JavaScript, and therefore a user browsing a malicious
site in Konqueror could trigger this issue. (Konqueror is not part of
a default install, but I've left this issue as critical in the results).
- Updates to correct all of these critical issues were available via Red Hat
Network within a day of the issues being public.
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 critical updates:
- A stack buffer overflow flaw in the RPC library in Kerberos.
This flaw was blocked by FORTIFY_SOURCE which removed the possibility of remote
code execution. We still issued an update,
as a remote attacker could trigger this flaw and cause Kerberos to crash.
- Another flaw in Kerberos, this time due to the free of an invalid
pointer. This flaw was blocked by glibc, although a remote attacker could still
cause
a crash, so we
issued an update.
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 metrics for any given Red Hat
product, package set, timescales, and severities.
Back in
August I found that many of the Common Vulnerability Scoring
System (CVSS) scores that the National Vulnerability Database (NVD)
assigned to vulnerabilities affecting open source software were incorrect.
Since then I've been sending in corrections on a monthly basis,
taking into account the worst possible score across all affected
platforms (and not how Red Hat products were affected specifically).
For the five months May to September 2007 I looked at 178
vulnerabilities (across all Red Hat products and services). Only 80
were accurate. Corrections were submitted to NVD and they fixed the
incorrect CVSS scores on the remaining 98 vulnerabilities.
So, before the corrections, there were 65 issues rated "High" out
of 178. After the corrections there are actually only 17 rated
"High". Fortunately the number of corrections needed each month
seems to be decreasing, but we'll continue to send in corrections
every month. Even with the corrections, the
severity rating for a given vulnerability may well vary for the
version each vendor ships; so you need to be careful if you are basing
your risk assesments soley on the accuracy of third-party severity ratings.
The National Vulnerability Database (NVD)
assign a severity rating to every vulnerability; "High", "Medium", or "Low".
The rating is determined by ranges of CVSS (Common Vulnerability Scoring System)
v2 scores. I've not been a big fan of CVSS: I don't think it works particularly
well when applied to software that is shipped by multiple vendors, or
for open source software and libraries that don't know all the possible
use-cases of their software.
Even though I'm not a fan, NVD publish a CVSS score for every issue,
security companies are using those scores in their vulnerability feeds to
customers, and people are using them for metrics. So it's important that
these scores are accurate.
I decided to take a look at how accurate the CVSS scores were, so for every
vulnerability we fixed in any Red Hat product for June 2007 examined the CVSS
score given by NVD. For each one figuring out if the CVSS base metrics were
correct, and where they were not submitting the correction back to NVD. This
analysis of the vulnerabilities was based on their possible worst-case threat to
all platforms (I didn't adjust the CVSS scores for how the issues affected Red
Hat products specifically).
There were 39 total vulnerabilities for which unfortunately only 8 scores were
accurate. I submitted corrections to NVD and they fixed the CVSS scores on the
remaining 31 vulnerabilities.
20 vulnerabilities ended up moving down in ranking, 6 vulnerabilities
moved up, and 5 stayed the same (although the CVSS score changed).
Before the corrections there were 14 issues rated "High" out of 39,
after the corrections there are just 3 rated "High".
Those corrections are now live in the NVD, and I really appreciate how quick the
folks behind NVD were at checking and making the changes. I've submitted to
them corrections for a couple more months too, and I'll write about those when
there complete. Unfortunately it does take a lot of time to investigate each
issue and do the corrections, so it will limit how far back into 2007
we can correct.
Although Red Hat is well known for Red Hat Enterprise Linux we actually have a large number of other supported products, both layered on top of Enterprise Linux (like Red Hat Application Stack) and stand-alone (like Red Hat Directory Server). The majority of these products are serviced through the Red Hat Network and get our security advisories in a standard way and are included in the Security Response Team metrics. But our analysis scripts were not particularly consistent in dealing with product names.
Common Platform Enumeration (CPE) is a naming scheme designed to combat these inconsistencies, and is part of the 'making security measurable' initiative from Mitre. From today we're supporting CPE in our Security Response Team metrics: we publish a mapping of Red Hat advisories to both CVE and CPE platforms (updated daily) and you can use CPE to filter the metrics. Some examples of CPE names:
cpe://redhat:enterprise_linux:5:server/firefox -- the Firefox browser package on Red Hat Enterprise Linux 5 server.
cpe://redhat:enterprise_linux:3 -- Red Hat Enterprise Linux 3
cpe://redhat/xpdf -- the xpdf package in any Red Hat
product.
cpe://redhat:rhel_application_stack:1 -- Red Hat Application Stack
version 1
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