Red Hat: RHSA-2009:1186-01 Critical: Nspr/Nss Security Fix

Netscape Portable Runtime (NSPR) provides platform independence for non-GUI operating system facilities. These facilities include threads, thread synchronization, normal file and network I/O, interval timing, calendar time, basic memory management (malloc and free), and shared library linking.
Network Security Services (NSS) is a set of libraries designed to support the cross-platform development of security-enabled client and server applications. Applications built with NSS can support SSLv2, SSLv3, TLS, and other security standards.
These updated packages upgrade NSS from the previous version, 3.12.2, to a prerelease of version 3.12.4. The version of NSPR has also been upgraded from 4.7.3 to 4.7.4.
Moxie Marlinspike reported a heap overflow flaw in a regular expression parser in the NSS library used by browsers such as Mozilla Firefox to match common names in certificates. A malicious website could present a carefully-crafted certificate in such a way as to trigger the heap overflow, leading to a crash or, possibly, arbitrary code execution with the permissions of the user running the browser. (CVE-2009-2404)
Note: in order to exploit this issue without further user interaction in Firefox, the carefully-crafted certificate would need to be signed by a Certificate Authority trusted by Firefox, otherwise Firefox presents the victim with a warning that the certificate is untrusted. Only if the user then accepts the certificate will the overflow take place.
Dan Kaminsky discovered flaws in the way browsers such as Firefox handle NULL characters in a certificate. If an attacker is able to get a carefully-crafted certificate signed by a Certificate Authority trusted by Firefox, the attacker could use the certificate during a man-in-the-middle attack and potentially confuse Firefox into accepting it by mistake. (CVE-2009-2408)
Dan Kaminsky found that browsers still accept certificates with MD2 hash signatures, even though MD2 is no longer considered a cryptographically strong algorithm. This could make it easier for an attacker to create a malicious certificate that would be treated as trusted by a browser. NSS now disables the use of MD2 and MD4 algorithms inside signatures by default. (CVE-2009-2409)
All users of nspr and nss are advised to upgrade to these updated packages, which resolve these issues and add an enhancement.