Vulnerability in Zulip
CVE-2026-40300
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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages.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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (27.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
- Zulip — versions < 12.0
- Zulip Server — versions 10.0
Weakness classification (CWE)
References
- github.com/zulip/zulip/security/advisories/GHSA-jp8f-mvv6-89cr (Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-40300?
- CVE-2026-40300 is a medium-severity vulnerability in Zulip, classified under Improper Access Control. CVSS score: 6.5/10. Published 2026-05-12.
- How severe is CVE-2026-40300?
- Medium severity. CVSS v3 base score is 6.5 out of 10.