What’s Vulnerable › Vulnerabilities

CVE-2021-41816

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 4.9% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2022-02-06 · updated 2026-06-17
• Weakness: CWE-190

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.

Affected products

• Fedoraproject Fedora: 34, 35
• ruby-lang CGI: before 0.3.1; through 0.2.0; through 0.1.0 — fixed in 0.3.1

How to fix

Upgrade to a fixed version: ruby-lang CGI 0.3.1. Check the vendor advisory for mitigations.

References

• https://hackerone.com/reports/1328463
• 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-2021-41816
• https://security.gentoo.org/glsa/202401-27
• https://security.netapp.com/advisory/ntap-20220303-0006/
• https://www.ruby-lang.org/en/news/2021/11/24/buffer-overrun-in-cgi-escape_html-cve-2021-41816/
• https://hackerone.com/reports/1328463
• 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-2021-41816
• https://security.gentoo.org/glsa/202401-27

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