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CVE-2021-20308

30
FAUCET Score

CVE-2021-20308 is an integer overflow vulnerability in htmldoc versions 1.9.11 and earlier, affecting Debian Linux and the htmldoc project. This critical vulnerability (CVSS 9.8) allows unauthenticated remote attackers to execute arbitrary code and cause a denial of service, similar to CVE-2017-9181, with low attack complexity. While the EPSS score is low and it's not on the KEV catalog, indicating a low likelihood of widespread exploitation, its high FAUCET Risk Score of 78/100 warrants attention. There is currently no public exploit code available (Metasploit, Nuclei, ExploitDB), and it has received no community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
<= 1.9.11CPE matchmatch criteria
cpe:2.3:a:htmldoc_project:htmldoc:*:*:*:*:*:*:*:*
9.0CPE matchmatch criteria
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.48%
Probability of exploitation in next 30 days
EPSS Percentile
82.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0248 is in the 73rd percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

bugzilla.redhat.com / show_bug.cgi
ExploitIssue TrackingThird Party Advisory
github.com / michaelrsweet/htmldoc/issues/423
ExploitIssue TrackingThird Party Advisory
lists.debian.org / debian-lts-announce/2021/07/msg00000.html
Mailing ListThird Party Advisory