Two serious security flaws have turned up in software widely distributed with Linux and Unix. The bugs affect Elm (Electronic Mail for Unix), a venerable e-mail client still used by many Linux and Unix sysadmins, and Mplayer, a cross-platform movie player that is one of the most popular of its kind on Linux.

The Elm flaw involves a boundary error when the client reads an e-mail's "Expires" header. A specially crafted e-mail could exploit the bug to cause a buffer overflow and execute malicious code on a system, according to security researchers.

Adding to the flaw's potential impact, exploit code has begun circulating on the Internet, according to FrSIRT, the French Security Incident Response Team, which published sample code on its site.

The flaw affects Elm version 2.5 PL7 and earlier, and has been fixed in a new update, version 2.5 PL8. A patched version is available via Elm-related websites, or from operating system vendors such as Red Hat.

Elm is one of the oldest email clients for Unix-like operating systems (including Linux), having gained popularity in the early 1990s. The application is a predecessor of such command-line e-mail clients as Mutt and Pine. Its users tend to be experienced Unix hands - the kind who run large, important systems, according to industry observers.

Red Hat, FrSIRT and advisory aggregator Secunia all gave the Elm flaw a highly critical rating.

The bug in Mplayer is the latest media-player bug to plague sysadmins. Widely used desktop applications such as media players are more difficult to patch than server-side bugs, because there are many times more copies in use, often without the knowledge of IT managers.

The flaw affects Mplayer versions 1.0pre7 and earlier, and hasn't been patched, according to an advisory from FrSIRT.

The flaw allows attackers to execute malicious code via a specially crafted media file, according to Sven Tantau, who discovered the flaw. The exploit is triggered by a specially crafted "strf" value in an audio header, and results in a buffer overflow, Tantau said in an advisory.