CVE-2026-40300

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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages.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.

CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0003

Probability of exploitation

0.10%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-284 CWE-284

Affected Products

Vendor	Product	Versions
zulip	zulip_server	All

References

Advisories & Patches

https://github.com/zulip/zulip/security/advisories/GHSA-jp8f-mvv6-89cr https://github.com/zulip/zulip/security/advisories/GHSA-jp8f-mvv6-89cr

Exploits

https://github.com/zulip/zulip/security/advisories/GHSA-jp8f-mvv6-89cr https://github.com/zulip/zulip/security/advisories/GHSA-jp8f-mvv6-89cr

Frequently Asked Questions

What is 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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages.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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-40300? +

CVE-2026-40300 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0003, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-40300? +

CVE-2026-40300 affects products from zulip, specifically: zulip_server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-40300? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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