Unix and Linux flaw leaves servers open to attack

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Unix and Linux flaw leaves servers open to attack

The Cert Co-ordination Centre security organisation has warned of a critical vulnerability affecting Unix and Linux systems.

The flaw is in the widely used Concurrent Versions System (CVS) software which could enable an unauthenticated remote attacker with read-only access to execute arbitrary code, alter program operation, read sensitive information or cause a denial of service to servers.

CVS is used by teams of software developers to co-ordinate their code writing and maintain a single standard view of the development process to all team members. It runs on several proprietary variants of Unix and on the open-source Linux OS.

It is a key tool for the open-source development community, and has been used in large-scale developments such as the Mozilla browser, the Python programming language, some versions of Linux such as ARM Linux, the freeDOS operating system and a Palm OS emulator.

CERT/CC described the vulnerability as a "double-free" vulnerability in the CVS server, whereby a set of specially crafted directory requests could cause an attempt to free a particular memory reference more than once.

This, in turn, could lead to heap corruption, which an attacker could use to execute arbitrary code, alter the logical operation of the CVS server program or read sensitive information stored in memory.

CERT/CC recommended users to disable anonymous CVS server access, or block or restrict access to CVS servers from untrusted hosts and networks until patches or upgrades can be applied.

Suppliers offering CVS with their Unix products, such as IBM, Sun Microsystems and Cray, as well as those of the principal Linux distributions, are offering patches for the flaw.

The most high-profile opponent of CVS as a development methodology is Linux founder Linus Torvalds, who uses an alternative system known as Bitkeeper to manage the development of the Linux kernel.

Torvalds has objected to the way that CVS maintains a central repository of the source code tree rather than giving all developers equal access to the code.

www.cert.org/advisories/CA-2003-02.html

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