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Fencer Vulns
high 7.8

CVE-2021-34121 json

An Out of Bounds flaw was discovered in htmodoc 1.9.12 in function parse_tree() in toc.cxx, this possibly leads to memory layout informatio…

published 2023-07-18 3 y ago modified 2026-06-17 4 mo ago also EUVD-2021-20784

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

An Out of Bounds flaw was discovered in htmodoc 1.9.12 in function parse_tree() in toc.cxx, this possibly leads to memory layout information leaking in the data. This might be used in a chain of vulnerability in order to reach code execution.

Patch / fix

  • htmldoc Debian 14, Debian 13, Debian 12 1.9.13-1

debian advisories DEBIAN-CVE-2021-34121

  • htmldoc Ubuntu Pro 14.04 LTS 1.8.27-8ubuntu1+esm3
  • htmldoc Ubuntu Pro 16.04 LTS 1.8.27-8ubuntu1.1+esm2
  • htmldoc Ubuntu Pro 18.04 LTS 1.9.2-1ubuntu0.2+esm1
  • htmldoc Ubuntu Pro 20.04 LTS 1.9.7-1ubuntu0.3+esm1

ubuntu advisories UBUNTU-CVE-2021-34121

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
2 y ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/michaelrsweet/htmldoc/issues/433 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Classification

Weakness

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.