Developers of the open-source GnuPG encryption software have reported a security flaw that could allow an attacker to sneak malicious code into a signed e-mail message.
GnuPG, or Gnu Privacy Guard, is an open-source version of the PGP encryption program used for encrypting data and creating digital signatures. It's included with several Linux distributions, including FreeBSD, and is also used widely used by the IT security industry.
The vulnerability allows an attacker to take a signed message and insert additional code, which then appears to the recipient as if it were part of the digitally signed content.
"Someone who's able to intercept the message as it's transmitted could inject some data, and then the person who verifies the signature would be told it's a valid, unaltered message," said Thomas Kristensen, chief technology officer with security vendor Secunia.
"That's one of the main purposes of the program, so it's quite significant," he added.
The attacker could potentially alter a text file, like a business contract, or an executable file attached to the message, he said. Secunia ranked the flaw as "moderately critical."
It affects all versions of GnuPG prior to 126.96.36.199, and users are advised to upgrade at once to that release. More information is on the GnuPG website.
The GnuPG team uncovered the flaw while testing the patch for a previous vulnerability. That flaw could have led to false positives when verifying signature files. Upgrading to the 188.8.131.52 release fixes that problem as well, the group said.
GPG is "fairly widely used among certain communities," although most people today probably use the encryption features in Microsoft Windows, Kristensen said.
The two recent security holes are unlikely to damage GPG's credibility, he said.
"People know it's still sound in the way it was designed and programmed, most people would consider this a minor oversight that's been corrected in a way you'd expect from a serious open-source project like GPG," Kristensen said.