Feeds

DoS risk from Zip of death attacks on AV software?

There's a heated debate

  • alert
  • submit to reddit

The Power of One eBook: Top reasons to choose HP BladeSystem

Claims that anti-virus and content filtering packages may be vulnerable to a denial of service attacks through maliciously constructed compressed archives have generated a heated debate in the security industry.

A discussion thread on BugTraq on the subject has prompted security consultants MIS Corporate Defence to issue an alert warning its customers of what it describes as an easy way of bringing networks to their knees.

Files are available on the Internet which are as little as 42KB in size but when fully decompressed have a total size of 16GB. The exploit works by sending an email containing such a maliciously formed compressed archive to an intended victim.

According to MIS, if restrictions are not in place an antivirus or content filtering system will attempt to fully decompress an archive in order to scan its contents, and this is where the trouble might kick in when the system is dealing with maliciously compressed archives.

However Graham Cluley of antivirus firm Sophos said that he believed most antivirus products would handle such files gracefully, stopping decompression long before systems run out of resources or disc space.

"If the file cannot be decompressed because of any resource issue then we gracefully decline to continue, and the file can be bunged into a 'quarantine' area if the user so chooses to set up the gateway product that way," said Cluley, who added that even under default setting Sophos's products are not vulnerable to this form of attack.

Cluley said it's incorrect to suggest that anti-virus software will attempt to decompress every file inside the archive before scanning, though he conceded that third party content filtering products might handle the decompression themselves and thereby be at risk.

Paul Rogers, a network security analyst at MIS, has carried out tests that show that the exploit can be used to crash systems running MAILsweeper filtering software from Content Technologies and antivirus products from F-Secure.

Rogers hadn't tested other products, so its unclear whether (for example) Symantec or Trend users are vulnerable, but he advised that best practice called for users to (where possible) restrict how many levels of compression their antivirus software would look into.

Although there has been little or no publicity about the issue, the potential vulnerability of antivirus products to a so-called Zip of death attack has been well known in security circles for some time. That said, the technique - for all the potential harm it might bring - has been little used by s'kiddies.

MessageLabs, a managed services firm that scans its user's email for viruses, reports that it had only seen two attempts at Zip of death attacks in the last year, which on both occasions it was able to detect and block. ®

Update

Network Associates has been in touch to tell us its products are not affected by the problem.

Related Stories

Flaw means virus could disable Norton Anti-Virus
Denial of service warning for network security tool
Virus toolkits are s'kiddie menace
Why Hotmail could spread viruses even faster than Outlook
Users haven't learned any lessons from the Love Bug
Reports of death of email viruses greatly exaggerated?
Rise in viruses within emails outpacing growth of email

The Power of One eBook: Top reasons to choose HP BladeSystem

More from The Register

next story
HIDDEN packet sniffer spy tech in MILLIONS of iPhones, iPads – expert
Don't panic though – Apple's backdoor is not wide open to all, guru tells us
BMW's ConnectedDrive falls over, bosses blame upgrade snafu
Traffic flows up 20% as motorway middle lanes miraculously unclog
LibreSSL RNG bug fix: What's all the forking fuss about, ask devs
Blow to bit-spitter 'tis but a flesh wound, claim team
Mozilla fixes CRITICAL security holes in Firefox, urges v31 upgrade
Misc memory hazards 'could be exploited' - and guess what, one's a Javascript vuln
Putin: Crack Tor for me and I'll make you a MILLIONAIRE
Russian Interior Ministry offers big pile o' roubles for busting pro-privacy browser
Manic malware Mayhem spreads through Linux, FreeBSD web servers
And how Google could cripple infection rate in a second
Don't look, Snowden: Security biz chases Tails with zero-day flaws alert
Exodus vows not to sell secrets of whistleblower's favorite OS
Researcher sat on critical IE bugs for THREE YEARS
VUPEN waited for Pwn2Own cash while IE's sandbox leaked
prev story

Whitepapers

Top three mobile application threats
Prevent sensitive data leakage over insecure channels or stolen mobile devices.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Top 8 considerations to enable and simplify mobility
In this whitepaper learn how to successfully add mobile capabilities simply and cost effectively.
Application security programs and practises
Follow a few strategies and your organization can gain the full benefits of open source and the cloud without compromising the security of your applications.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.