Zlib Security Flaw Exposes Swath of Programs

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Security

A serious security flaw has been identified in Zlib, a widely used data compression library. Fixes have begun to appear, but a large number of programs could be affected.

Zlib is a data compression library that is used by many third-party programs and is distributed with many operating systems, including many Linux and BSD distributions.

Microsoft Corp. and other proprietary software companies also use the library in many programs. These companies can do so because Zlib is licensed under liberal BSD-style license.

This isn't the first time that the popular Zlib has been the center of a security concern. In 2002, a problem with how it handled memory allocation became a major concern.

This time, the flaw is a buffer overflow in the decompression process. Because the program doesn't properly validate input data, it can be fed bad data, which can lead to a buffer overflow.

This, in turn, means that if a user opens a file with a Zlib-enabled application, such as a Web browser or data compression tool, which contains specially malformed compressed data, an attacker could execute arbitrary code as the user. If this user were running as a system administrator the flaw would run at that level as well.

Since Zlib is so ubiquitous, this represents a serious security concern.

It's not clear how many programs are affected, but some operating system distributions are widely exposed. According to one source, numerous key packages in the Fedora Core 3 distribution use Zlib. Symantec Corp. reports that AIX, Debian, FreeBSD, Gentoo, SuSE, Red Hat, Ubuntu and many other operating systems are affected.

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UPDATE: Linux vendors pump out highly critical patch.