Approximately 20,000 websites have been compromised with code that could allow a user's system to be exploited remotely, Symantec security researchers have warned.
The attacks, which began on Tuesday, originally involved two Chinese sites hosting exploits for the flaw: wuqing17173.cn and woai117.cn. Further analysis by Symantec indicated another domain involved: dota11.cn.
Malicious code is being injected into third-party domains, probably through SQL-injection attacks. The code then redirects users to sites hosting malicious Flash files, according to an advisory on Symantec's SecurityFocus site.
The code exploits a flaw in Adobe Flash Player version 126.96.36.199, and may affect 188.8.131.52, said Symantec. Other versions of Flash Player may also be affected, Symantec warned. The flaw, which appears to be a buffer overflow vulnerability, occurs when Flash Player processes a malicious Shockwave Flash (SWF) file. Normally SWF files contain animations or interactive applications.
An attacker can use the Flash files to execute whatever code they like (arbitrary code) on the system remotely. Even failed exploit attempts would probably lead to denial-of-service conditions, according to Symantec.
The Sans Institute has reported a further attack, involving the play0nlnie.com domain. The attack generates URLs designed to target specific Flash version and browser combinations, including Internet Explorer and Firefox.
There are no vendor patches as yet. However, the Adobe Product Security Incident Response Team is investigating the issue, according to a blog post.
Update: Following the posting of this article, the Adobe Product Security Incident Response Team issued this statement:
"This exploit appears to be taking advantage of a known vulnerability, reported by Mark Dowd of the ISS X-Force and wushi of team509, that was resolved in Flash Player 184.108.40.206 (CVE-2007-0071). We strongly encourage everyone to download and install the latest Flash Player update, 220.127.116.11."