In a , Microsoft acknowledged the disclosure earlier in the day of an exploit of long-known bugs in the used to create the digital certificates that in turn provide proof of a secure connection between users and Web sites. But the software vendor minimized the danger that users could face.
"This new disclosure does not increase risk to customers significantly, as the researchers have not published the cryptographic background to the attack, and the attack is not repeatable without this information," said Microsoft. The company added that it wasn't aware of any actual attacks using the techniques described by an international team of researchers from Germany, the Netherlands, Switzerland and the U.S.
Microsoft also noted that most of the certificate authority vendors that issue digital certificates have abandoned MD5 and upgraded to the more secure SHA-1 algorithm.
However, there are several notable exceptions that still rely on MD5, including 's RapidSSL.com certificate authorization scheme. The researchers, who presented their findings at a security conference in Berlin today, said they in fact were able to hack RapidSSL.com and produce fake digital certificates.
A more stringent class of digital certificates, dubbed Extended Validation, are always signed using SHA-1, Microsoft added. "As such, [they] are not affected by this newly reported research," the company's advisory read.
Extended Validation, or EV certificates, are supported by all current Web browsers, which display a special icon or shade the address bar when the user surfs to a site secured by one. Microsoft's own , for instance, turns the entire address bar green when it encounters a site secured by an EV certificate, while 's tints part of its address bar the same color.
Although Microsoft didn't offer any specific steps for users to take to protect themselves in light of today's disclosures, it urged them to keep Windows updated with the latest software patches.
Microsoft wasn't the only company that responded to the news about the exploit of the MD5 bug. Earlier today, that the MD5 algorithm could be hacked and that phony digital certificates could be created as a result.
"This is not an attack on a Mozilla product, but we are nevertheless working with affected certificate authorities to ensure that their issuing processes are updated to prevent this threat," Johnathan Nightingale, a Mozilla spokesman on security issues, wrote in an entry posted on the company's blog. Like Microsoft's advisory, Nightingale's warning also said that Mozilla hadn't seen any evidence of actual attacks.
Even so, Nightingale recommended that Firefox users remain watchful. "We advise users to exercise caution when interacting with sites that require sensitive information, particularly when using public Internet connections," he wrote.