CVE-2021-41816

Exp

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.

Published: 2022-02-06 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]

NVD Status：Modified，CVE State: published

View at NVD, CVE.org, EUVD

Threat Intelligence & Risk Assessment for CVE-2021-41816

EPSS CVSS CWE GHSA Exploit-DB Affected OS Tracker

Conclusion & alert: CVE-2021-41816 is rated High Exploit Risk (90.2/100): CVSS Critical severity, with high exploitation likelihood (EPSS 4.77%, 91th percentile). Core evidence: 1 public exploit reference(s) are indexed (Exploit-DB). EPSS rose +4.28% over the last day, indicating growing attacker interest. Mandatory action: Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-41816

EDB-ID	Source	Kind	Published	Link
—	nvd_ref	exploit_tag		Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-41816

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.48%	4.77%	+4.28%
2	2026-04-16	0.44%	0.48%	+0.04%
3	2026-03-07	—	0.44%	—

Full EPSS history (56 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-41816

CVSS metrics for this CVE.

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
7.5	2.0	HIGH	`AV:N/AC:L/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	10.0	6.4	[email protected]

Weakness enumeration for CVE-2021-41816

CWE-190 MITRE ↗

GitHub Security Advisory for CVE-2021-41816

GHSA-5cqm-crxm-6qpv · Severity: critical · Ecosystem: rubygems — Buffer overrun in CGI.escape_html

OS Trackers for CVE-2021-41816

vendor	priority	summary	link
`alpine`	—	CVE-2021-41816: 1 source package rows (ruby); 8 state rows across 8 repos (3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 0.	https://security.alpinelinux.org/vuln/CVE-2021-41816
`debian`	not yet assigned	CVE-2021-41816 not yet assigned priority: Debian including 1 source packages (ruby2.7), 1 status rows across 1 suites (bullseye): resolved 1.	https://security-tracker.debian.org/tracker/CVE-2021-41816
`gentoo`	normal	CVE-2021-41816: 1 GLSA(s) (202401-27), 1 atom(s) (dev-lang/ruby); latest impact normal.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-41816
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-41816
`ubuntu`	medium	CVE-2021-41816 medium priority: Ubuntu including 4 source packages (ruby2.3, ruby2.5, ruby2.7, ruby3.0), 17 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): ignored 7, needs-triage 4, released 4, not-affected 2.	https://ubuntu.com/security/CVE-2021-41816

Affected software / configurations for CVE-2021-41816

Vendor	Product	Version	Raw CPE
ruby-lang	cgi	< 0.3.1	cpe:2.3:a:ruby-lang:cgi::::::ruby::*
ruby-lang	cgi	<= 0.2.0	cpe:2.3:a:ruby-lang:cgi::::::ruby::*
ruby-lang	cgi	<= 0.1.0	cpe:2.3:a:ruby-lang:cgi::::::ruby::*
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*
fedoraproject	fedora	35	cpe:2.3:o:fedoraproject:fedora:35:::::::*

References for CVE-2021-41816

URL	Tags
https://hackerone.com/reports/1328463	Permissions 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-2021-41816	Third 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

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