Hacker tips CERT's hand on Linux/PDF flaw 
By Paul Roberts
IDG News Service
June 16, 2003    
Confidential vulnerability information managed by the CERT
Coordination Center has again been leaked to the public, following a
flurry of such leaks in March.

The latest information concerns a flaw in PDF (Portable Document 
Format) readers for Unix and could allow a remote attacker to trick 
users into executing malicious code on their machines, according to a 
copy of the leaked vulnerability report. 

As with confidential CERT information that was leaked in March, the 
latest report was posted to a vulnerability discussion list by an 
individual using the name "hack4life." 

The leaked information was taken from communication sent from CERT to 
software vendors affected by the PDF problem, according to Jeffrey 
Carpenter, manager of the CERT Coordination Center. The information 
appears to be from a vulnerability report submitted to CERT by a 
Cincinnati security researcher by the name of Martyn Gilmore. 

Gilmore did not respond to requests for comment and CERT would not 
comment on how it obtained the PDF vulnerability information or on 
Gilmore's relationship with the Pittsburgh-based software 
vulnerability monitoring organization. 

In the report, Gilmore describes a problem in the way that PDF viewing 
programs for the Unix platform process hyperlinks within valid PDF 
documents. When processing hyperlinks, common PDF readers use the Unix 
"shell" command (sh -c) to launch and pass commands to external 
programs. For example, clicking on a hyperlink for a Web page would 
launch the associated Web browser, according to the report. 

However, Gilmore found that such programs do not properly check the 
syntax of such commands, enabling arbitrary shell commands to be 
executed on the vulnerable machine. 

While attackers are limited by the privilege level of the user 
clicking the malicious link, the vulnerability could enable a remote 
attacker to use shell commands to delete files from the user's hard 
drive or perform other actions without the knowledge of the victim, 
the report said. 

Adobe Systems Inc.'s Acrobat Reader 5.06 is affected by the problem in 
addition to the open-source reader Xpdf 1.01, according to the report. 

CERT declined to discuss the details of the vulnerability.

The vulnerability information was scheduled to be released by CERT on 
June 23, according to an e-mail message purporting to be from 
hack4life that prefaced the leaked report. 

The release date was obtained from CERT communications with its 
vendors, as well, but CERT declined to comment on whether it would be 
releasing an advisory regarding the PDF problem on June 23, according 
to Carpenter. 

Hack4life cited "college and exams" for the lull in leaked CERT 
information in recent months and hinted at the likelihood of more 
disclosures in the future. 

"I'll have plenty of time to keep you all up to date with what those 
fools at CERT are up to once college is finished," hack4life wrote. 

In March, someone using the same name posted information on four 
vulnerabilities that CERT was investigating to the vulnerability 
discussion list Full-Disclosure. Those posts included sensitive 
information on a vulnerability in the Kerberos Version 4 protocol and 
a problem reported by Microsoft Corp. regarding spammers' abuse of Web 
redirectors, which forward users of Web portals such as MSN IP 
(Internet Protocol) addresses close to their geographic location. 

The PDF information was disclosed to CERT after the vulnerabilities 
were leaked in March, Carpenter said.

Contacted by e-mail in March, hack4life denied any affiliation with 
CERT and said that the reports were "stolen in a recent computer 

"Fun and amusement" was the primary motivation for stealing and 
leaking the vulnerability reports. A secondary motivation cited in 
e-mail by hack4life was anger over CERT's perceived failure to publish 
vulnerability information in a timely manner. 

At the time, CERT officials cast doubt on hack4life's assertion that 
the reports were hacked, saying that the information was most likely 
leaked by a member of one of the development teams CERT works with to 
evaluate vulnerabilities. 

The latest incident reaffirms CERT's belief that the problem lies with 
its vendors rather than with its own systems, Carpenter said. While 
CERT does not yet know which vendor is responsible for the leak, the 
organization is confident that an insider threat or compromise at one 
of the companies it deals with is responsible for the leaks, he said. 

CERT is communicating with vendors about the problem, but Carpenter 
would not comment on whether CERT is working with law enforcement to 
catch the person responsible for the leaks. 

"I'm not going to get into those specifics at this point," he said.

CERT plans to consult with affected vendors and discuss how to proceed 
now that the information is public, he said.

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