GitHub on Monday informed users that it had discovered what it described as an “extremely rare, but potentially serious” security bug related to how some authenticated sessions were handled.
The Microsoft-owned software development platform said the issue was discovered on March 2 and an initial patch was rolled out on March 5. A second patch was released on March 8 and on the evening of the same day the company decided to invalidate all authenticated sessions to completely eliminate the possibility of exploitation.
The vulnerability, which GitHub said existed at various times between February 8 and March 5, was caused by a race condition that in extremely rare circumstances resulted in a user’s session being routed to the browser of a different authenticated user, providing this second user with a valid and authenticated session cookie for the first user’s account.
“It is important to note that this issue was not the result of compromised account passwords, SSH keys, or personal access tokens (PATs) and there is no evidence to suggest that this was the result of a compromise of any other GitHub systems,” noted Mike Hanley, GitHub’s recently appointed chief security officer. “Instead, this issue was due to the rare and isolated improper handling of authenticated sessions. Further, this issue could not be intentionally triggered or directed by a malicious user.”
Hanley said they learned about the issue as a result of an external report about anomalous behavior.
Less than 0.001% of authenticated sessions on GitHub.com were impacted and the company said there was no evidence that other products were affected.
“Out of an abundance of caution, and with a strong bias toward account security, we’ve invalidated all sessions on GitHub.com created prior to 12:03 UTC on March 8 to avoid even the remote possibility that undetected compromised sessions could still exist after the vulnerability was patched,” Hanley explained.