An attacker had access to a privileged account on Mozilla’s Bugzilla bug tracker for at least a year and is believed to have accessed the details of 185 non-public vulnerabilities before the breach was discovered.
According to Mozilla, the attacker downloaded information on vulnerabilities affecting Firefox and other Mozilla products after obtaining the credentials of a privileged Bugzilla user. The targeted user had apparently set the same password on at least another website that was breached.
Logs showed that the intruder had access since September 2014, but there are some indications that the account may have been compromised since as far back as September 2013.
Mozilla said the attacker accessed 185 private bugs, 110 of which were not security related. Of the remaining 75 issues, 22 were classified as low or moderate severity issues, while the other 53 were rated as having high or critical impact.
Fortunately, 43 of the high and critical vulnerabilities had already been fixed by the time the attacker learned about them. On the other hand, it’s possible that the remaining ten security holes have been leveraged in attacks against Firefox users because they were patched only days, weeks or even months after the attacker learned of their existence. The longest vulnerability window was 335 days, Mozilla said.
The web browser vendor claims to have evidence of only one attack leveraging an exposed vulnerability. On August 6, the company updated Firefox to version 39.0.3 after learning that a zero-day flaw in the browser had been exploited on a Russian news website to steal sensitive information from users.
The two vulnerabilities patched by Mozilla on August 27 with the release of version 40.0.3 were the last ones that could have been exploited by the attacker against Firefox users.
The compromised Bugzilla account was shut down as soon as the breach was discovered and Mozilla’s security team launched an investigation to determine the extent of the incident. A forensic analysis was also conducted by an external security firm hired by Mozilla.
“We are updating Bugzilla’s security practices to reduce the risk of future attacks of this type. As an immediate first step, all users with access to security-sensitive information have been required to change their passwords and use two-factor authentication,” explained Richard Barnes of Mozilla’s Security Engineering team. “We are reducing the number of users with privileged access and limiting what each privileged user can do. In other words, we are making it harder for an attacker to break in, providing fewer opportunities to break in, and reducing the amount of information an attacker can get by breaking in.”
This is not the first Bugzilla-related security incident. In August 2014, Mozilla warned that the email addresses and encrypted passwords of 97,000 users who had tested Bugzilla builds were dumped on a public server.