CVE-2021-30479

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-04-15 · updated 2026-06-17
Weakness: CWE-269

Description

An issue was discovered in Zulip Server before 3.4. A bug in the implementation of the all_public_streams API feature resulted in guest users being able to receive message traffic to public streams that should have been only accessible to members of the organization.

Affected products

zulip: before 3.4 — fixed in 3.4

How to fix

Upgrade to a fixed version: zulip 3.4. Check the vendor advisory for mitigations.

References

https://blog.zulip.com/2021/04/14/zulip-server-3-4/
https://blog.zulip.com/2021/04/14/zulip-server-3-4/

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