CVE-2026-40300 Zulip: Message edit history visible in "moves only" policy through /api/v1/messages/{id}/history
Low-privilege users can recover edited message content via API despite restrictive visibility policies, exposing sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-40300?
CVE-2026-40300 is a medium-severity vulnerability in zulip, published on 12 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Zulip is an open-source team collaboration tool. Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages. This vulnerability is fixed in 12.0.
Weakness: CWE-284
Which versions are affected by CVE-2026-40300?
It affects 1 product.
Products include Zulip Zulip Server.
How do I fix CVE-2026-40300?
No fix has been published for CVE-2026-40300 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-40300 being exploited?
There is no known exploitation of CVE-2026-40300 in the wild and no public exploit code.
Other vulnerabilities in zulip
- CVE-2019-18933 Information disclosure in n/a
- CVE-2020-15070 Code injection in n/a
- CVE-2017-0910 Missing authorization in Zulip Server
- CVE-2025-31478 Zulip Authentication Backend Configuration Bypass
- CVE-2023-33186 Cross-site scripting vulnerability in Zulip Server development branch via topic tooltip
Sources
Also known as GHSA-jp8f-mvv6-89cr.