CVE-2021-3866

Name: CVE-2021-3866
Creator: NVD / NIST
Published: 2022-01-20T11:15:07.927+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.4/10EPSS 0.89%

Last modified Jun 17, 2026

CVE-2021-3866 is a medium-severity vulnerability rated 5.4/10 on the CVSS scale. Cross-site Scripting (XSS) - Stored in GitHub repository zulip/zulip more than and including 44f935695d452cc3fb16845a0c6af710438b153d and prior to 3eb2791c3e9695f7d37ffe84e0c2184fae665cb6.. EPSS estimates a 0.89% chance of exploitation in the next 30 days.

Description

Cross-site Scripting (XSS) - Stored in GitHub repository zulip/zulip more than and including 44f935695d452cc3fb16845a0c6af710438b153d and prior to 3eb2791c3e9695f7d37ffe84e0c2184fae665cb6.

Metrics

CVSS 3.1

5.4/10

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

EPSS Probability

0.89%

54.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Zulip	Zulip	<= 4.8

References

https://blog.zulip.com/2022/01/19/cve-2021-3866/Vendor Advisory
https://github.com/zulip/zulip/commit/3eb2791c3e9695f7d37ffe84e0c2184fae665cb6Patch, Third Party Advisory
https://huntr.dev/bounties/5f48dac5-e112-4b23-bbbf-cc00ba83bcf2Exploit, Third Party Advisory
https://blog.zulip.com/2022/01/19/cve-2021-3866/Vendor Advisory
https://github.com/zulip/zulip/commit/3eb2791c3e9695f7d37ffe84e0c2184fae665cb6Patch, Third Party Advisory
https://huntr.dev/bounties/5f48dac5-e112-4b23-bbbf-cc00ba83bcf2Exploit, Third Party Advisory

Timeline

Published: Jan 20, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-3866?

Cross-site Scripting (XSS) - Stored in GitHub repository zulip/zulip more than and including 44f935695d452cc3fb16845a0c6af710438b153d and prior to 3eb2791c3e9695f7d37ffe84e0c2184fae665cb6.

How severe is CVE-2021-3866?

CVE-2021-3866 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.89% probability of exploitation in the next 30 days.

How do I fix CVE-2021-3866?

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-2021-3866?

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

Scan your code now

Source: NVD / NIST