The glibc packages contain the standard C libraries used by multiple programs on the system. These packages contain the standard C and the standard math libraries. Without these two libraries, a Linux system cannot function properly.
An integer overflow flaw, leading to a heap-based buffer overflow, was found in the way the glibc library read timezone files. If a carefully-crafted timezone file was loaded by an application linked against glibc, it could cause the application to crash or, potentially, execute arbitrary code with the privileges of the user running the application. (CVE-2009-5029)
A denial of service flaw was found in the remote procedure call (RPC) implementation in glibc. A remote attacker able to open a large number of connections to an RPC service that is using the RPC implementation from glibc, could use this flaw to make that service use an excessive amount of CPU time. (CVE-2011-4609)
This update also fixes the following bugs:
glibc had incorrect information for numeric separators and groupings for specific French, Spanish, and German locales. Therefore, applications utilizing glibc's locale support printed numbers with the wrong separators and groupings when those locales were in use. With this update, the separator and grouping information has been fixed. (BZ#754116)
The RHBA-2011:1179 glibc update introduced a regression, causing glibc to incorrectly parse groups with more than 126 members, resulting in applications such as "id" failing to list all the groups a particular user was a member of. With this update, group parsing has been fixed. (BZ#766484)
glibc incorrectly allocated too much memory due to a race condition within its own malloc routines. This could cause a multi-threaded application to allocate more memory than was expected. With this update, the race condition has been fixed, and malloc's behavior is now consistent with the documentation regarding the MALLOC_ARENA_TEST and MALLOC_ARENA_MAX environment variables. (BZ#769594)
Users should upgrade to these updated packages, which contain backported patches to resolve these issues.