By Gregg Keizer
December 22, 2008

Microsoft Corp.'s developers missed a critical bug in Internet Explorer because they weren't properly trained and didn't have the right testing tools, a noted proponent of the company's secure code development process acknowledged last week.

The bug, which Microsoft patched last week with an emergency update, had gone undetected for at least nine years. In an insider's description on Microsoft's Security Development Lifecycle blog, Michael Howard, a principal security program manager at the company, offered a postmortem analysis of the IE vulnerability and Microsoft's code-writing and reviewing process.

Howard, who is perhaps best known for co-authoring the book Writing Secure Code, said the flaw was a "time-of-check-time-of-use" bug in how IE releases data binding objects. The vulnerability was not found by programmers because they had not been told or taught to look for them in such cases, Howard said. "Memory-related [time-of-check-time-of-use, or TOCTOU] bugs are hard to find through code review," he said.

"We teach TOCTOU issues, and we teach memory corruption issues, and issues with using freed memory blocks; but we do not teach memory-related TOCTOU issues." Microsoft's testing tools -- including "fuzzers," which are automated tools that drop data into applications, file formats or operating system components to see if and where they fail -- also missed the bug, Howard acknowledged.