Microsoft said on Tuesday that it is investigating reports of a zero-day vulnerability affecting Windows 7 and Vista.
The flaw in Windows 7 could allow an attack which would cause a critical system error, or "blue screen of death," according to researcher Laurent Gaffie.
Gaffie wrote in his blog that the flaw lies in a Server Message Block 2 (SMB2) driver.
"SRV2.SYS fails to handle malformed SMB headers for the NEGOTIATE PROTOCOL REQUEST functionality," wrote Gaffie in a blog post Monday.
Gaffie said he had contacted Microsoft. Comments on his blog by other users said that the flaw could lead not only to denial of service, but could also lead to remote code execution.
Microsoft said in a statement on Tuesday that it was investigating, but said it is "currently unaware of any attacks trying to use the claimed vulnerability or of customer impact."
Computer security publication "The H" wrote on Tuesday that its German sister publication had tested the proof-of-concept code, and that while the exploit had caused a reboot on Vista, the exploit had not worked on Windows 7.
Metasploit creator HD Moore said in a tweet on Tuesday that an SMB bug appeared to have been introduced into Vista SP1. Coder Josh Goebel said in a blog post that he had added the exploit code to Metasploit.
Tom Espiner of ZDNet UK reported from London. CNET News' Ina Fried contributed to this report.