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Fencer Vulns
critical 9.8

CVE-2021-3466 json

A flaw was found in libmicrohttpd.

published 2021-03-25 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26788

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
8.7%
EPSS 8.7% chance of exploitation in 30 days, percentile 95%
public exploits
0
none known

Summary

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.

Patch / fix

  • libmicrohttpd Debian 14, Debian 13, Debian 12 0.9.71-1

debian advisories DEBIAN-CVE-2021-3466

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3466 updated cvss 8.1

libmicrohttpd: Buffer overflow issue in URL parser in the post_process_urlencoded function

  • Red Hat Enterprise Linux 6 libmicrohttpd Red Hat Enterprise Linux 7 libmicrohttpd Red Hat Enterprise Linux 8 libmicrohttpd Red Hat Enterprise Linux 9 libmicrohttpd
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

8.74% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 10.0 AV:N/AC:L/Au:N/C:C/I:C/A:C

Affected products

  • n/a libmicrohttpd

Classification

Weakness
  • CWE-120 Buffer Copy without Checking Size of Input

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.