So you may have gotten a Slack password reset prompt. Something like half a percent of Slack’s userbase had their password hash potentially exposed due to an odd bug. When sending shared invitation links, the password hash was sent to other members of the workspace. It’s a bit hard to work out how this exact problem happened, as password hashes shouldn’t ever be sent to users like this. My guess is that other users got a state update packet when the link was created, and a logic error in the code resulted in too much state information being sent.

The evidence suggests that the first person to catch the bug was a researcher who disclosed the problem mid-July. Slack seems to use a sane password policy, only storing hashed, salted passwords. That may sound like a breakfast recipe, but just means that when you type your password in to log in to slack, the password goes through a one-way cryptographic hash, and the results of the hash are stored. Salting is the addition of extra data, to make a precomputation attack impractical. Slack stated that even if this bug was used to capture these hashes, they cannot be used to directly authenticate as an affected user. The normal advice about turning on 2-factor authentication still applies, as an extra guard against misuse of leaked information. Continue reading “This Week In Security: Breaches, ÆPIC, SQUIP, And Symbols” →