CVE-2021-40647: In man2html 1.6g, a specific string being read in from a file will overwrite the size parameter in the top chu

Routine

MEDIUM 5.5DOWNGRADE

CVE-2021-40647 is a medium-severity flaw (CVSS 5.5) affecting man2html. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In man2html 1.6g, a specific string being read in from a file will overwrite the size parameter in the top chunk of the heap. This at least causes the program to segmentation abort if the heap size parameter isn't aligned correctly. In version before GLIBC version 2.29 and aligned correctly, it allows arbitrary write anywhere in the programs memory.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 73%)
CISA exploited list	No
Weakness	CWE-787
Published	2022-09-09
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: man2html project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-09-09 18:15 UTCPublished CVE record published
2026-06-17 04:07 UTCUpdated Record last modified

man2html project man2html DOWNGRADE

Affected: 1.6g

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.6g

1. Check installed version

apt-cache policy man2html || rpm -q man2html || man2html --version

2. No fixed release: DOWNGRADE to a release before 1.6g (Debian / Ubuntu)

apt-cache madison man2html sudo apt install man2html=<VERSION_BEFORE_1.6g> sudo apt-mark hold man2html

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list man2html sudo dnf downgrade man2html-<VERSION_BEFORE_1.6g> sudo dnf versionlock add man2html

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-40647?

man2html: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-40647 being exploited?

CVE-2021-40647 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-40647 affect?

CVE-2021-40647 affects man2html. Severity is medium (CVSS 5.5). In man2html 1.6g, a specific string being read in from a file will overwrite the size parameter in the top chunk of the heap. This at least causes the program to segmentation abort if the heap size parameter isn't aligned correctly. In vers

How urgent is CVE-2021-40647?

Priority 31/100. Public exploit reference

Software pages

glibc vulnerabilities

Related CVEs

CVE-2021-40648 MEDIUM 5.5 DOWNGRADE In man2html 1.6g, a filename can be created to overwrite the previous size parameter of the next chunk and the

References

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