The vulnerability, reported last month by Ernst & Young security researcher Nitesh Dhanjani, was related to the fact that the web browser did not require user permission prior to a download. When he contacted Apple to report the issue, the company told him it did not intend to patch the glitch because it did not deem the bug a security concern.
Apple changed its mind when it issued Thursday's security update for Safari 3.1.2 for Windows.
"Saving an untrusted file to the Windows desktop may trigger the issue, and lead to the execution of arbitrary code," Apple said in its security update. "Web browsers are a means by which files may be saved to the desktop. To help mitigate this issue, the Safari browser has been updated to prompt the user prior to saving a download file."
Esler said a blended attack could occur if a victim visited a malicious website through the Safari for Windows browser. Users, in theory, could download a malicious DLL (dynamically linked library) to the desktop, without their permission, and then Internet Explorer would automatically execute the DLL.
"The two vulnerabilities together made one massive problem," he said.
Proof-of-concept exploit code had been published.
Microsoft, in a security advisory issued May 30, suggested users stop using Safari for Windows until Apple issued a fix.
"You can't just have Microsoft coming out and saying your browser is insecure," he said. "They've got to react. They've got to do something."
Thursday's security update from Apple includes fixes for three other, less critical vulnerabilities in Safari for Windows.
An Apple spokeswoman did not respond to a request for comment.