Firm finds danger in dangling pointers

Microsoft's Security Response Centre also had other problems. Less than two weeks later, zero-day details on a vulnerability in the handling of the Windows Meta File (WMF) format had leaked to the Internet, and the software giant had to scramble to develop a patch.

The software giant fixed the IIS flaw as part of its regularly schedule Patch Tuesday on 10 July. The software giant would only comment on the patch, not the flaw itself.

Security researchers have known that dangling pointers can be an exploitable vulnerability; it is not a new concept.

Last week, security firm iDefense published details on an exploitable dangling pointer flaw in the Opera web browser. The vulnerability was caused by the browser's misuse of application memory when removing BitTorrent transfers from the transfer list.

Determining whether such vulnerabilities can be exploited is not a trivial task, said Sean Larsson, security intelligence engineer for Internet and security services firm VeriSign, iDefense' parent company.

"There are more reported buffer overflow vulnerabilities than dangling pointer vulnerabilities," Larsson stated in an e-mail interview with SecurityFocus. "However, that doesn't necessarily mean that dangling pointer vulnerabilities are not common. Depending on the behaviour of the program, a dangling pointer vulnerability might not even result in a crash, which makes it difficult to detect."

Opera patched the vulnerability in an update released last week in coordination with iDefense's announcement.

Watchfire called such announcements the "tip of the iceberg".

The security-audit firm would give few details before the Black Hat presentation, but did say that the applications most in danger are web servers and operating systems, followed by client software used to access the internet, such as web browsers. Also, programming languages that automatically clean up memory when an object is deleted - called implicit garbage collection - will not be affected by dangling pointers.

"It is very technical and sophisticated, more so than exploiting a buffer overflow," Allan said. "Any application that is remotely accessible to me is my biggest target. Any software that does not have implicit garbage collection is going to be a target."

"My guess is there will be a lot of research into dangling pointers in the future," he said.

This article originally appeared in Security Focus.

Copyright © 2007, SecurityFocus