Microsoft Corp.'s Internet Explorer browser has an unpatched vulnerability that could let hackers hijack, then access, Google Inc. Gmail accounts, a security company warned yesterday.
IE, said Cenzic in an alert issued Monday, contains an unspecified cached-files bug that, when combined with a cross-site request forgery flaw (CSRF) in the Web-based e-mail service, exposes Gmail account sign-ons and lets others access those accounts and any messages or file attachments there. According to Cenzic, IE sports "improper use of caching directives [and] incorrect access checks on cached Internet Explorer files."
Although not a bug that can be leveraged remotely -- an attacker must have local, physical access to the PC -- as Cenzic pointed out in its alert, there are scenarios where that's not a limitation. "These vulnerabilities could be exploited such that all users of a shared computer, who use Internet Explorer and share a user account -- a common practice at computer kiosks in a library or Internet cafe -- could be vulnerable," said Cenzic.
Gmail, Cenzic went on, contributes to the overall vulnerability because its URLs display attachments when viewed using the "View Source" command.
Together, the bugs could conceivably let someone at a public PC hijack any Gmail log-on credentials that had been entered on the machine since the IE cache had last been purged. IE deletes the contents of its cache only as new files are added -- the oldest are deleted -- or when the user explicitly instructs the browser to clear the cache using the "Delete Browsing History" command.
Microsoft quickly denied that IE had a bug. "Microsoft has thoroughly investigated the claim and found that this is not a product vulnerability," said a company spokesman in an e-mail today. "In the scenario in question, an attacker would need authenticated access to the system in order to modify files located in the cache," the spokesman continued. "With that level of access, an attacker could install malicious programs that would have more impact than the scenarios described."
While true, the spokesman's explanation did not address Cenzic's scenario; by design, public PCs such as those in libraries, schools or Web cafes do not require authentication for users to access them. A Microsoft representative was not available for clarification.
Google also rejected Cenzic's claim, using reasoning similar to Microsoft's explanation.
"In this case, a malicious user using a shared computer could alter the environment, in this scenario, modify data in the local browser cache, to make it hostile for all subsequent users," said a Google spokeswoman. "But this is not specific to Gmail or Google products. A malicious user could exploit a shared computer any number of more direct ways, [for example] by installing a user-mode keylogger."