Zlib is a general-purpose lossless data compression library which is used by many different programs.
Tavis Ormandy discovered a buffer overflow affecting Zlib version 1.2 and above. An attacker could create a carefully crafted compressed stream that would cause an application to crash if the stream is opened by a user. As an example, an attacker could create a malicious PNG image file which would cause a web browser or mail viewer to crash if the image is viewed. The Common Vulnerabilities and Exposures project assigned the name CAN-2005-2096 to this issue.
Please note that the versions of Zlib as shipped with Red Hat Enterprise Linux 2.1 and 3 are not vulnerable to this issue.
All users should update to these erratum packages which contain a patch from Mark Adler which corrects this issue.