The GnuTLS library provides support for cryptographic algorithms and for protocols such as Transport Layer Security (TLS).
A flaw was found in the way the TLS/SSL (Transport Layer Security/Secure Sockets Layer) protocols handled session renegotiation. A man-in-the-middle attacker could use this flaw to prefix arbitrary plain text to a client's session (for example, an HTTPS connection to a website). This could force the server to process an attacker's request as if authenticated using the victim's credentials. This update addresses this flaw by implementing the TLS Renegotiation Indication Extension, as defined in RFC 5746. (CVE-2009-3555)
Refer to the following Knowledgebase article for additional details about the CVE-2009-3555 flaw: http://kbase.redhat.com/faq/docs/DOC-20491
Dan Kaminsky found that browsers could 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. GnuTLS now disables the use of the MD2 algorithm inside signatures by default. (CVE-2009-2409)
Users of GnuTLS are advised to upgrade to these updated packages, which contain backported patches to correct these issues. For the update to take effect, all applications linked to the GnuTLS library must be restarted, or the system rebooted.