CVE-2021-41816

Name: CVE-2021-41816
Creator: NVD / NIST
Published: 2022-02-06T21:15:07.887+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 4.77%

Last modified Jun 17, 2026

CVE-2021-41816 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. CGI.escape_html in Ruby before 2.7.5 and 3.x before 3.0.3 has an integer overflow and resultant buffer overflow via a long string on platforms (such as Windows) where size_t and long have different numbers of bytes. This also affects the CGI gem before 0.3.1 for Ruby.. EPSS estimates a 4.77% chance of exploitation in the next 30 days.

Description

CGI.escape_html in Ruby before 2.7.5 and 3.x before 3.0.3 has an integer overflow and resultant buffer overflow via a long string on platforms (such as Windows) where size_t and long have different numbers of bytes. This also affects the CGI gem before 0.3.1 for Ruby.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

4.77%

90.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-190

Affected Software

Vendor	Product	Versions
Ruby-Lang	Cgi	< 0.3.1
Ruby-Lang	Cgi	<= 0.2.0
Ruby-Lang	Cgi	<= 0.1.0
Fedoraproject	Fedora	34
Fedoraproject	Fedora	35

References

https://hackerone.com/reports/1328463Permissions Required, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IUXQCH6FRKANCVZO2Q7D2SQX33FP3KWN/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UTOJGS5IEFDK3UOO7IY4OTTFGHGLSWZF/
https://security-tracker.debian.org/tracker/CVE-2021-41816Third Party Advisory
https://security.gentoo.org/glsa/202401-27
https://security.netapp.com/advisory/ntap-20220303-0006/Third Party Advisory
https://www.ruby-lang.org/en/news/2021/11/24/buffer-overrun-in-cgi-escape_html-cve-2021-41816/Exploit, Vendor Advisory
https://hackerone.com/reports/1328463Permissions Required, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IUXQCH6FRKANCVZO2Q7D2SQX33FP3KWN/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/UTOJGS5IEFDK3UOO7IY4OTTFGHGLSWZF/
https://security-tracker.debian.org/tracker/CVE-2021-41816Third Party Advisory
https://security.gentoo.org/glsa/202401-27
https://security.netapp.com/advisory/ntap-20220303-0006/Third Party Advisory
https://www.ruby-lang.org/en/news/2021/11/24/buffer-overrun-in-cgi-escape_html-cve-2021-41816/Exploit, Vendor Advisory

Timeline

Published: Feb 6, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-41816?

How severe is CVE-2021-41816?

CVE-2021-41816 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 4.77% probability of exploitation in the next 30 days.

How do I fix CVE-2021-41816?

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-2021-41816?

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

Scan your code now

Source: NVD / NIST