Flaw Endangers Debian-Based Encryption Keys

Officials with the Debian Project recommend that users re-create all cryptographic key material generated by OpenSSL versions starting with 0.9.8c-1.

Enterprises may face an uphill battle to address the fallout from a recently disclosed vulnerability affecting Debian-based Linux distributions that allows hackers to brute-force their way past encryption.

The flaw, which was reported May 13 by the Debian Project, rests in the random number generator, which is used to produce cryptographic keys. The vulnerability allows an attacker to use brute-force guessing attacks to decipher keys used in SSH (Secure Shell), DNSSEC (Domain Name System Security Extensions), OpenVPN, X.509 certificates, and session keys used in SSL/TLS (Secure Sockets Layer/Transport Layer Security) connections.

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The vulnerability has been present since September of 2006. In an advisory, officials with the Debian Project recommended that all cryptographic key material generated by OpenSSL versions starting with 0.9.8c-1 on Debian systems be re-created from scratch, and that all DSA keys ever used on affected Debian systems for signing or authentication purposes be considered compromised.

"It is a big deal to patch and then have to regenerate keys-that is why we always say look for FIPS [Federal Information Processing Standard] 140-tested crypto, which would tests things like the random number generator," said John Pescatore, an analyst with Gartner.

The Debian Project has released an update for OpenSSL, as well as information on key rollover procedures and a tool that can detect weak keys.

Nick Selby, an analyst with The 451 Group, noted that the vulnerability affects not only Debian, but distributions based on it such as Ubuntu.

"The upgrade is crucial to users of products like OpenSSH and the session keys used in SSL/TLS connections and other encryption software that relies on the random number generator in Debian's OpenSSL package," Selby said.

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Complicating the situation is that tools for exploiting the flaw are already circulating in the wild. Security researcher HD Moore, who created the Metasploit penetration testing framework, claimed on his Web site that he was able to generate 1024- and 2048-bit keys for x86 in about 2 hours. In addition, information on a working exploit for Debian-generated SSH keys was posted to the Full-Disclosure mailing list May 15.

"There's actually a number of vulnerabilities," said David Frazer, director of technology services at F-Secure. "There's vulnerabilities specifically related to exploiting for denial-of-service attacks. There's the weak keys, but there's also the issue of where a key has been generated and then imported into another system-then that by definition has also made that other system vulnerable."