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Vulnerabilities

Vulnerability · CVE-2026-40300

Zulip is an open-source team collaboration tool.

Published May 12, 2026 · catalog updated Jun 17, 2026 · zulip server

Check if you run it

No confirmed exploitation is on record for CVE-2026-40300. EPSS is 0.35%. Act only if a listed version of zulip server is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.0
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.35%
Remediation
Advisory link
Affected products
cpe zulip/zulip server

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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages.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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe zulip/zulip server10.0

How to fix CVE-2026-40300

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-40300. EPSS is 0.35%. Act only if a listed version of zulip server is installed.

Which versions are affected?

Compare what you have installed with zulip/zulip server 10.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-284: Improper Access Control. EPSS 0.35%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. May 12, 2026 · NIST NVD

    Detected

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Prior to 12.0, With message_edit_history_visibility_policy set to "moves", /api/v1/messages/{id}/history still returns historical content values, allowing low-privilege users to recover text that was edited away from other users' messages.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

  2. Jun 17, 2026 · NIST NVD

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2026-40300

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-40300

    30-day exploitation probability 0.4%

    first.org
  • NIST NVDVulnerability recordCVE-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' m

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.