Crackers owned the primary file servers of the GNU Project from mid-March until two weeks ago, the Free Software Foundation admitted this week.
The attack raises concerns about whether malicious code could have been inserted in the software available for download, including some Linux applications.
However, evidence suggests no source code distributions were modified as a result of the attack. Current files have all been validated by the FSF, which oversees the GNU Project.
Nonetheless sites using software obtained from the compromised system are urged to verify the integrity of their distribution. FSF is providing software hashes to this end which can be found here.
The attack took place in March using a zero-day exploit, but was only discovered in late July. FSF replaced the compromised machine in early August.
In a statement, the FSF explained: "A root compromise and a Trojan horse were discovered on gnuftp.gnu.org, the FTP server of the GNU project. The machine appears to have been cracked in March 2003, but we only discovered the crack in the last week of July 2003. The modus operandi of the cracker shows that (s)he was interested primarily in using gnuftp to collect passwords and as a launching point to attack other machines."
"It appears that the machine was cracked using a ptrace exploit by a local user immediately after the exploit was posted," it added.
Evidence found on the compromised machine indicates that gnuftp was cracked during the week between the release of the ptrace bug, a root-shell exploit, and the time a working fix for the Linux-kernel was available a week later.
The FSF have tightened up security defences since the attack. Local shell access to the FTP server for GNU maintainers has been withdrawn pending completion of its certification activities.
Security clearing house CERT has also issued an advisory on the attack.
It far from the first time crackers have broken into the web servers of software developers. In May 2001, infamous cracker Fluffy Bunny bragged that he had compromised the systems of the Apache project.
In October 2000, Microsoft's systems were comprehensively compromised by a cracker using the QAZ Trojan. Weeks later Microsoft's core web sites were again 0wn3d in an attack that went beyond the usual Web page defacement. ®
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