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Vulnerabilities

Vulnerability · CVE-2026-100404

Zulip is an open-source team collaboration tool.

Published Oct 14, 2026 · catalog updated Oct 14, 2026 · Zulip is an open-source

Check if you run it

No confirmed exploitation is on record for CVE-2026-100404. EPSS is 0.41%. Act only if a listed version of Zulip is an open-source is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Zulip is an open-source).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.41%
Remediation
Advisory link
Affected products
See sources for product scope

Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages from an unsubscribed public channel, or an existing event queue can remain affected after the guest's access to the channel is removed. The flaw discloses new public-channel messages to the guest. This issue is fixed in version 12.2.

No affected version ranges are stored yet. Use the vendor advisory before you decide this record does not apply.

How to fix CVE-2026-100404

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-2026-100404. EPSS is 0.41%. Act only if a listed version of Zulip is an open-source is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-862: Missing Authorization. EPSS 0.41%. 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.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 14, 2026 · NIST NVD

    Detected

    Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages from an unsubscribed public channel, or an existing event queue can remain affected after the guest's access to the channe

Sources

  • CVE.orgVulnerability recordCVE-2026-100404

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-100404

    30-day exploitation probability 0.4%

    first.org
  • NIST NVDVulnerability recordCVE-2026-100404

    Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages fr

    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.