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Watch out, office bods: A backdoor daemon lurks in HP LaserJets

Aah, telnet. We meet again

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A range of HP LaserJet printers suffer a security flaw that can leak data and passwords, the US Computer Emergency Response Team (CERT) warns. Users have been told to apply the firmware patches issued by HP that resolve the issue.

HP says the security risk arose after it was discovered that several models of HP LaserJets feature a "telnet debug shell which could allow a remote attacker to gain unauthorized access to data". Essentially, this means the printers can be accessed through a telnet session without requiring a password - allowing unauthenticated remote attackers to gain access to unencrypted data using this telnet daemon.

Security bods have suggested that HP's developers mistakenly left the debugging aid in the firmware of the affected printers.

"Debugging code is an all-but-unavoidable part of any development project, aimed at helping you to understand more precisely how your code behaves internally," explained Paul Ducklin, Sophos's head of technology for Asia Pacific, in a blog post.

"This often means that debugging code is a security nightmare, since it may allow software behaviour which is unsuitable for a shipping product, such as introspection (a fancy word for peeking inside data structures that are usually off limits to other users), and authentication bypasses. So, debug code is typically compiled out altogether in a release build."

Ducklin added that Telnet is "unencrypted, insecure and out of place in 2013".

HP has patched the afflicted firmware for the affected printers. Users of a wide range of HP printers are advised to apply the update. It listed the vulnerable kit as: HP LaserJet Pro P1102w, HP LaserJet Pro P1606dn, HP LaserJet Pro M1213nf MFP, HP LaserJet Pro M1214nfh MFP, HP LaserJet Pro M1216nfh MFP, HP LaserJet Pro M1217nfw MFP. HP HotSpot LaserJet Pro M1218nfs MFP, HP LaserJet Pro M1219nf MFP, HP LaserJet Pro CP1025nw and HP LaserJet Pro CP1025nw.

HP's advisory (support document) is here. German security researcher Christoph von Wittich of Hentschke Bau gets the hat tip for finding the vulnerabilities. ®

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