CVE-2021-43791

Name: CVE-2021-43791
Creator: NVD / NIST
Published: 2021-12-02T01:15:07.423+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.64%

Last modified Jun 17, 2026

CVE-2021-43791 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Zulip is an open source group chat application that combines real-time chat with threaded conversations. In affected versions expiration dates on the confirmation objects associated with email invitations were not enforced properly in the new account registration flow. EPSS estimates a 0.64% chance of exploitation in the next 30 days.

Description

Zulip is an open source group chat application that combines real-time chat with threaded conversations. In affected versions expiration dates on the confirmation objects associated with email invitations were not enforced properly in the new account registration flow. A confirmation link takes a user to the check_prereg_key_and_redirect endpoint, before getting redirected to POST to /accounts/register/. The problem was that validation was happening in the check_prereg_key_and_redirect part and not in /accounts/register/ - meaning that one could submit an expired confirmation key and be able to register. The issue is fixed in Zulip 4.8. There are no known workarounds and users are advised to upgrade as soon as possible.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.64%

46.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-613

Affected Software

Vendor	Product	Versions
Zulip	Zulip	< 4.8

References

https://github.com/zulip/zulip/commit/a014ef75a3a0ed7f24ebb157632ba58751e732c6Patch, Third Party Advisory
https://github.com/zulip/zulip/security/advisories/GHSA-wj76-pcqr-mf9fThird Party Advisory
https://github.com/zulip/zulip/commit/a014ef75a3a0ed7f24ebb157632ba58751e732c6Patch, Third Party Advisory
https://github.com/zulip/zulip/security/advisories/GHSA-wj76-pcqr-mf9fThird Party Advisory

Timeline

Published: Dec 2, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-43791?

How severe is CVE-2021-43791?

CVE-2021-43791 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.64% probability of exploitation in the next 30 days.

How do I fix CVE-2021-43791?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-43791?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST