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.

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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text…

EPSS: 0.000 (10.2th percentile) — read the EPSS interpretation.

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.

Affected products

Zulip — versions < 12.0
Zulip Zulip_server — versions 10.0

Weakness classification (CWE)

CWE-284 — Improper Access Control

References

security-advisories@github.com (x_refsource_CONFIRM, 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.