Race condition in Zulip

Vulnerability Description

Zulip is an open source group chat application. Starting with version 4.0 and prior to version 4.11, Zulip is vulnerable to a race condition during account deactivation, where a simultaneous access by the user being deactivated may, in rare cases, allow continued access by the deactivated user. A patch is available in version 4.11 on the 4.x branch and version 5.0-rc1 on the 5.x branch. Upgrading to a fixed version will, as a side effect, deactivate any cached sessions that may have been leaked through this bug. There are currently no known workarounds.

References

• https://github.com/zulip/zulip/security/advisories/GHSA-6v98-m5x5-phqj
• https://github.com/zulip/zulip/commit/62ba8e455d8f460001d9fb486a6dabfd1ed67717
• https://github.com/zulip/zulip/commit/e6eace307ef435eec3395c99247155efed9219e4