CVE-2021-3466

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2022-05-24. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 9%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A flaw was found in libmicrohttpd. A missing bounds check in the post_process_urlencoded function leads to a buffer overflow, allowing a remote attacker to write arbitrary data in an application that uses libmicrohttpd. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability. Only version 0.9.70 is vulnerable.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
52(Track)
EG Risk 52/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation9% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
94.6%
KEV
Not listed

Published

March 25, 2021

Last Modified

November 21, 2024

Advisory Details (5)

Auto-updated Jul 1, 2026
Patch available. Sources: redhat.
generic

GNU Libmicrohttpd: Buffer Overflow Vulnerability (GLSA 202311-08) — Gentoo security

https://security.gentoo.org/glsa/202311-08
generic

[SECURITY] Fedora 33 Update: libmicrohttpd-0.9.73-1.fc33 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K5NEPVGP3L2CZHLZ4UB44PEILHKPDBOG/
generic

[SECURITY] Fedora 34 Update: libmicrohttpd-0.9.73-1.fc34 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/75HDMREKITMGPGE62NP7KE62ZJVLETXN/
generic

[SECURITY] Fedora 32 Update: libmicrohttpd-0.9.73-1.fc32 - package-announce - Fedora mailing-lists

https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4334XJNDJPYQNFE6S3S2KUJJ7TMHYCWL/
redhat Patch Available

1939127 – (CVE-2021-3466) CVE-2021-3466 libmicrohttpd: Buffer overflow issue in URL parser in the post_process_urlencoded function

Affected: Red Hat Enterprise Linux 6, 7, and 8 as the vulnerable code was only introduced in later versions of the library.

https://bugzilla.redhat.com/show_bug.cgi?id=1939127

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 50× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 108 total refreshes for this CVE.

  1. 2026-07-23 14:16 UTCEPSS rescore
  2. 2026-07-23 02:01 UTCEG score recompute
  3. 2026-07-22 22:48 UTCEG score recompute
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Frequently asked(5)

What is CVE-2021-3466?
CVE-2021-3466 is a critical vulnerability published on March 25, 2021. A flaw was found in libmicrohttpd. A missing bounds check in the postprocessurlencoded function leads to a buffer overflow, allowing a remote attacker to write arbitrary data in an application that uses libmicrohttpd. The highest threat from this vulnerability is to data confidentiality and…
When was CVE-2021-3466 disclosed?
CVE-2021-3466 was first published in the National Vulnerability Database on March 25, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-3466 actively exploited?
CVE-2021-3466 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 94.6% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-3466?
CVE-2021-3466 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-3466?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3466, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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