CVE-2021-43799

What it is

Zulip is an open-source team collaboration tool. Zulip Server installs RabbitMQ for internal message passing. In versions of Zulip Server prior to 4.9, the initial installation (until first reboot, or restart of RabbitMQ) does not successfully limit the default ports which RabbitMQ opens; this includes port 25672, the RabbitMQ distribution port, which is used as a management port. RabbitMQ's default "cookie" which protects this port is generated using a weak PRNG, which limits the entropy of the password to at most 36 bits; in practicality, the seed for the randomizer is biased, resulting in approximately 20 bits of entropy. If other firewalls (at the OS or network level) do not protect port 25672, a remote attacker can brute-force the 20 bits of entropy in the "cookie" and leverage it for arbitrary execution of code as the rabbitmq user. They can also read all data which is sent through RabbitMQ, which includes all message traffic sent by users. Version 4.9 contains a patch for this vulnerability. As a workaround, ensure that firewalls prevent access to ports 5672 and 25672 from outside the Zulip server.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure.

Exploit odds

5.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2022-01-25 21:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:11 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 5.4% in the next 30 days (EPSS).
• Severity: 8.6 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2022-01-25 21:15 UTC

Last modified

2026-06-17 04:11 UTC

Exploit probability

5.4% · EPSS, next 30 days

Weakness

CWE-338

Record status

Modified

Affected

• Zulip < 4.9

Attack profile CVSS 3.1 · 8.6

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-43799.md and follow it. Check whether this project is affected by CVE-2021-43799. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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