The first exploit code takes advantage of a "critical" flaw in the Windows Dynamic Host Configuration Protocol, or DHCP, client, according to a customer alert sent out by the French Security Incident Response Team on Monday. Microsoftfor the problem, Symantec said in its own advisory for subscribers.
An attacker could gain full control over an unpatched Windows computer using the exploit, Symantec said.
Microsoft tackled the problem in security bulletin MS06-036, and people who have applied that update are protected, a representative for the software maker said.
The second, proof-of-concept code targets a security hole in a Windows component called "mailslot," which Microsoft patched in bulletin MS06-035, Symantec and FRSIRT said. However, Microsoft said it believes the code takes advantage of a new flaw.
"Proof-of-concept code was published on the Internet for a variant of the vulnerabilities addressed by Microsoft security update MS06-035," the representative for the software maker said. The company is monitoring this situation and may issue another patch, to fix the variant, the representative said.
Security experts pointed to the "mailslot" vulnerability as the most risky in Microsoft's July patch bunch. It could be used to spread a worm, they warned. However, the proof-of-concept code released over the weekend does not have as severe an effect; all it can do is crash a computer, Symantec said.
Microsoft said it is not aware of any actual attacks that use either of the two exploit code samples, the representative said.
The company issued seven security bulletins with fixes for 18 flaws earlier this month. At least two of the vulnerabilities were already being exploited in attacks prior to the patches being released, security company iDefense has said. Also, soon, miscreants launched attacks .