Kaspersky has exposed a security loophole in Apple's Safari web browser.
The browser stores authentication credentials used in earlier web sessions in a plaintext XML file known as a property list, which it can refer to to restore web pages if the browser is closed.
The details remain unencrypted and are stored in a standard plist file that is accessible to anyone.
Kaspersky Lab Global Research and Analysis Team researcher Vyacheslav Zakorzhevsky said that the complete authorised session on the site is saved in the plist file in full view despite the use of https.
"The file itself is located in a hidden folder, but is available for anyone to read," Zakorzhevsky said. "We're ready to bet that it won't be long before it appears."
The firm has already notified Apple of the vulnerability.
Currently two versions of Apple's operating systems are affected by the issue, including OSX10.8.5, Safari 6.0.5 (8536.30.1) and OSX10.7.5, Safari 6.0.5 (7536.30.1).
The security firm also added that the 'Reopen All Windows from Last Session' option found on the browser would open sites they had left in the earlier session.
"You can just imagine what would happen if cybercriminals or a malicious program got access to the LastSession.plist file on a system where the user logs in to Facebook, Twitter, LinkedIn or their online bank account," Zakorzhevsky added.
"As far as we are concerned, storing unencrypted confidential information with unrestricted access is a major security flaw that gives malicious users the opportunity to steal user data with a minimum of effort."