CVE-2026-100404: Auth Bypass (CVSS 6.5)

Description

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.

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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

0.0042

Probability of exploitation

0.34%

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-862 Missing Authorization

References

Other References

https://github.com/zulip/zulip/commit/98659a41cb93d4ce329ea14bb0cdfb4b147500ba https://github.com/zulip/zulip/commit/c03db8916456674df3c98614f6f0ef8cd024ef11 https://github.com/zulip/zulip/pull/39913 https://github.com/zulip/zulip/releases/tag/12.2 https://github.com/zulip/zulip/security/advisories/GHSA-5r8f-gq2h-fcgp

Frequently Asked Questions

What is CVE-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 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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-100404? +

CVE-2026-100404 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 0.0042, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-100404? +

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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