The code execution vulnerability, revealed on Friday, affects the current version (4.0.5) of Safari for Windows and could allow an attacker to compromise a user's system. Other versions of the browser could also be affected.
Users are being advised to avoid visiting untrusted websites or clicking on links from untrusted sources.
The vulnerability is the result of, 'an error in the handling of parent windows and can result in a function call using an invalid pointer,' according to Secunia's advisory. The vulnerability could be exploited to execute arbitrary code if a user is directed to a specially crafted web page and attempts to close pop-up windows.
Secunia has rated the vulnerability 'highly critical', or four out of five on its severity rating scale.
The vulnerability also likely affects Safari for Mac because the code base of the two programs is largely the same, according to Mac security firm Intego.
"We're keeping an eye on this to see how it progresses, as this is the kind of vulnerability that can be exploited when a user simply visits a web page," Peter James, spokesman at Intego, wrote in a blog post on Monday.
He said: “For now, this is reported on Safari 4.0.5 for Windows, but it is highly possible that it affects the Mac version as well, since the two programs share a large part of their code base."