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Vulnerability record · CVE-2021-43791 · published 2 December 2021

CVE-2021-43791: Zulip insufficient session expiration vulnerability

Zulip · Zulip

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.

5.3 CVSS 3.1 Medium EPSS 0.66% · top 50.3% CWE-613 · Insufficient session expiration
5.3CVSS 3.1 base score, v2 5.0
0.66%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/zulip/zulip/commit/a014ef75a3a0ed7f24ebb157632ba58751e732c6 PatchThird Party Advisory
https://github.com/zulip/zulip/security/advisories/GHSA-wj76-pcqr-mf9f Third Party Advisory
https://github.com/zulip/zulip/commit/a014ef75a3a0ed7f24ebb157632ba58751e732c6 PatchThird Party Advisory
https://github.com/zulip/zulip/security/advisories/GHSA-wj76-pcqr-mf9f Third Party Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-43791), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.