Microsoft has fessed up to hiding details on software vulnerabilities discovered internally, insisting that full disclosure of every security-related product change only aids attackers.
The admission follows criticisms from a security researcher that the policy of silently fixing software flaws is "misleading" and not in the spirit of Microsofts push for transparency.
Mike Reavey, operations manager of the Microsoft Security Response Center, said the Redmond, Wash., companys policy is to document the internally discovered flaws and the area of functionality where the change occurred but that full details on the fixes are withheld for a very good reason: to protect customers.
Critics argue that silent fixes can hurt businesses that depend on information from the vendor to determine deployment time frames and the actual severity of the patched vulnerability.
According to eEye Digital Security, which sells host-based IPS (intrusion prevention system) technology, silent fixes from Microsoft are commonplace. "We routinely find them," said Steve Manzuik, product manager of eEyes security research team, in Aliso Viejo, Calif.
Manzuik said Microsoft has been silently fixing bugs since as far back as 2004. He referred to the companys MS04-007 bulletin as a classic example of Microsoft announcing a fix for a single vulnerability when, in fact, a total of seven flaws were quietly fixed.
Manzuiks team presented a paper on its findings at the Black Hat Briefings in Europe earlier in 2006 to highlight problems with withholding fix details from customers.
"When details arent included, [administrators] wont install [a] patch," Manzuik said.
Manzuik said IT departments lack skills or resources to reverse-engineer every patch. "They are simply left in the dark and may ignore a patch that is supercritical to their environment. Meanwhile, the bad guy has spent the time to find out what was silently fixed," he said.
Matthew Murphy, the independent researcher who flagged the issue after finding silent fixes in the April batch of patches, said third-party vendors that incorporate code from Microsoft also are hurt by the lack of full disclosure. Murphy outlined a recent case in which anti-virus vendor Trend Micro got burned by a silent fix of Microsofts. The issue involved a bug in Visual Studio that was reported to Microsoft in 2002 but remained unfixed for several years.
Withheld information caused Trend Micro to unwittingly use vulnerable code in its products, putting its customers at risk of a heap overflow vulnerability that could be used in code execution attacks.
Manzuik also pointed out that businesses rely heavily on host-based IPS technology to secure valuable assets while patches are being tested for deployment. "How can you create a signature for a flaw if you dont know the location of the flaw?" Manzuik said.
Reavey said businesses should use Microsofts severity rating system to help with patch deployment timetables. "Its important to remember that the best way to be safe and secure is to apply all the updates," he said.