RHSA-2012:0306 - Security Advisory

Topic

Updated krb5 packages that fix one security issue and various bugs are now
available for Red Hat Enterprise Linux 5.

The Red Hat Security Response Team has rated this update as having low
security impact. A Common Vulnerability Scoring System (CVSS) base score,
which gives a detailed severity rating, is available from the CVE link in
the References section.

Description

Kerberos is a network authentication system which allows clients and
servers to authenticate to each other using symmetric encryption and a
trusted third-party, the Key Distribution Center (KDC).

It was found that ftpd, a Kerberos-aware FTP server, did not properly drop
privileges. On Red Hat Enterprise Linux 5, the ftpd daemon did not check
for the potential failure of the effective group ID change system call. If
the group ID change failed, a remote FTP user could use this flaw to gain
unauthorized read or write access to files that are owned by the root
group. (CVE-2011-1526)

Red Hat would like to thank the MIT Kerberos project for reporting this
issue. Upstream acknowledges Tim Zingelman as the original reporter.

This update also fixes the following bugs:

• Due to a mistake in the Kerberos libraries, a client could fail to

contact a Key Distribution Center (KDC) or terminate unexpectedly if the
client had already more than 1024 file descriptors in use. This update
backports modifications to the Kerberos libraries and the libraries use
the poll() function instead of the select() function, as poll() does not
have this limitation. (BZ#701444)

• The KDC failed to release memory when processing a TGS (ticket-granting

server) request from a client if the client request included an
authenticator with a subkey. As a result, the KDC consumed an excessive
amount of memory. With this update, the code releasing the memory has been
added and the problem no longer occurs. (BZ#708516)

• Under certain circumstances, if services requiring Kerberos

authentication sent two authentication requests to the authenticating
server, the second authentication request was flagged as a replay attack.
As a result, the second authentication attempt was denied. This update
applies an upstream patch that fixes this bug. (BZ#713500)

• Previously, if Kerberos credentials had expired, the klist command could

terminate unexpectedly with a segmentation fault when invoked with the -s
option. This happened when klist encountered and failed to process an entry
with no realm name while scanning the credential cache. With this update,
the underlying code has been modified and the command handles such entries
correctly. (BZ#729067)

• Due to a regression, multi-line FTP macros terminated prematurely with a

segmentation fault. This occurred because the previously-added patch failed
to properly support multi-line macros. This update restores the support for
multi-line macros and the problem no longer occurs. (BZ#735363, BZ#736132)

All users of krb5 are advised to upgrade to these updated packages, which
resolve these issues.

Solution

Before applying this update, make sure all previously-released errata
relevant to your system have been applied.

This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
https://access.redhat.com/kb/docs/DOC-11259

Affected Products

• Red Hat Enterprise Linux Server 5 x86_64
• Red Hat Enterprise Linux Server 5 ia64
• Red Hat Enterprise Linux Server 5 i386
• Red Hat Enterprise Linux Workstation 5 x86_64
• Red Hat Enterprise Linux Workstation 5 i386
• Red Hat Enterprise Linux Desktop 5 x86_64
• Red Hat Enterprise Linux Desktop 5 i386
• Red Hat Enterprise Linux for IBM z Systems 5 s390x
• Red Hat Enterprise Linux for Power, big endian 5 ppc
• Red Hat Enterprise Linux Server from RHUI 5 x86_64
• Red Hat Enterprise Linux Server from RHUI 5 i386

Fixes

• BZ - 701444 - Fix libkrb5 to work when > 1024 file descriptors are in use
• BZ - 708516 - memory leak during kdc TGS request
• BZ - 711419 - CVE-2011-1526 krb5, krb5-appl: ftpd incorrect group privilege dropping (MITKRB5-SA-2011-005)
• BZ - 729067 - klist -s segfaults with expired credentials
• BZ - 750823 - Newly introduced defect into krb5

CVEs

• CVE-2011-1526

References

• https://access.redhat.com/security/updates/classification/#low
• http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-005.txt