CVE-2021-36773

Name: CVE-2021-36773
Creator: NVD / NIST
Published: 2021-07-18T04:15:08.11+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.26%

Last modified Jun 17, 2026

CVE-2021-36773 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. uBlock Origin before 1.36.2 and nMatrix before 4.4.9 support an arbitrary depth of parameter nesting for strict blocking, which allows crafted web sites to cause a denial of service (unbounded recursion that can trigger memory consumption and a loss of all blocking functionality).. EPSS estimates a 1.26% chance of exploitation in the next 30 days.

Description

uBlock Origin before 1.36.2 and nMatrix before 4.4.9 support an arbitrary depth of parameter nesting for strict blocking, which allows crafted web sites to cause a denial of service (unbounded recursion that can trigger memory consumption and a loss of all blocking functionality).

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

1.26%

65.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-674

Affected Software

Vendor	Product	Versions
Sciruby	Nmatrix	< 4.4.9
Ublockorigin	Ublock Origin	< 1.36.2
Umatrix Project	Umatrix	< 1.4.2
Debian	Debian Linux	9.0

References

https://github.com/vtriolet/writings/blob/main/posts/2021/ublock_origin_and_umatrix_denial_of_service.adocExploit, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/06/msg00024.htmlMailing List, Third Party Advisory
https://news.ycombinator.com/item?id=27833752Issue Tracking, Third Party Advisory
https://github.com/vtriolet/writings/blob/main/posts/2021/ublock_origin_and_umatrix_denial_of_service.adocExploit, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/06/msg00024.htmlMailing List, Third Party Advisory
https://news.ycombinator.com/item?id=27833752Issue Tracking, Third Party Advisory

Timeline

Published: Jul 18, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-36773?

How severe is CVE-2021-36773?

CVE-2021-36773 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.26% probability of exploitation in the next 30 days.

How do I fix CVE-2021-36773?

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-2021-36773?

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

Scan your code now

Source: NVD / NIST