A bug in Windows Vista’s built-in email program can be used by hackers to run malicious code on a victimised PC, according to a researcher who last month touted an exploit-for-sale service.
Microsoft acknowledged the report, and says it is investigating the vulnerability.
Symantec’s DeepSight network, which issued a warning about the vulnerability in Windows Mail, later upped the threat rating from 6.8 to 7.5 in a follow-up alert after it confirmed that the bug was remote code exploitable. That means an attacker could introduce his or her own malware onto a compromised computer. Windows Mail is the successor to Outlook Express, the entry-level email application that’s been bundled with the operating system since the Windows 95 edition.
By crafting an email message with a link to a malicious file — one hosted on a remote internet server, say — and duping the recipient into clicking on the link, an attacker could infect a Vista PC with software that steals identities or with a backdoor Trojan horse.
In some cases, all that’s required is that the user clicks on the link, says Symantec. “An attacker can deliver an email message containing a malicious link that references a local executable,” the DeepSight alert says.
“If the victim clicks on this link, the native program is executed with no further action required. For instance: an attacker could achieve the execution of the local file ‘winrm.cmd.’”
If run, “winrm.cmd” — the Windows Remote Management command-line tool — would give an attacker complete access to a PC.
If the link points to a malicious file not on the PC, the user has one more chance to figure out the scam, adds Symantec. “If the user follows [this] link, they are presented with a dialogue box where they must click ‘Yes’, to open the file. Once the user clicks ‘Yes’ the file opens or executes with the privileges of that user.”
Microsoft’s Security Response Centre (MSRC) team downplayed the potential risk. “Microsoft is not aware of any attacks attempting to use the reported vulnerability or of customer impact at this time,” MSRC says.
It’s possible that could change. The researcher who disclosed the bug and posted exploit code on the Full Disclosure security mailing list also announced an exploit-for-sale service nearly three weeks ago on the same list.
On March 11, the researcher, who goes by the moniker “Kingcope”, posted a message on Full Disclosure touting the new service.
“We now have our exploit-selling site up and running ... [where] you can purchase quality advisories and exploits. Feel free to contact our sales person for getting the latest zero-days,” Kingcope wrote.
The website referenced in Kingcope’s message was unavailable for a time, and sported a “The system is down for maintenance” message. Kingcope did not respond to emails requesting details of the bug-for-sale service.
Both Symantec and Microsoft urged users not to click links in unsolicited email, while the former also recommends users disable HTML within Windows Mail.
As is its practice, Microsoft says it may issue an additional advisory, or patch the problem in a future — but unspecified — security update. The next scheduled patch release date for Microsoft products, including Vista, is April 10.
Coincidentally, it was only last week that an executive in Microsoft’s security technology unit boasted about Vista and gave the new operating system an A-plus for security in its first 90 days of release.