How severe is CVE-2021-20308?

CVE-2021-20308 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-20308 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20308?

CVE-2021-20308 primarily affects Htmldoc Project Htmldoc. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-20308?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-20308 published?

CVE-2021-20308 was published on 2021-04-05 and last updated on 2026-06-17.

CVE-2021-20308

CVE-2021-20308 is a critical-severity vulnerability in Htmldoc Project Htmldoc with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-190.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (83rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-190
Affected product: Htmldoc Project Htmldoc
Published: 2021-04-05
Last modified: 2026-06-17

Description

Integer overflow in the htmldoc 1.9.11 and before may allow attackers to execute arbitrary code and cause a denial of service that is similar to CVE-2017-9181.

Frequently asked questions

What is CVE-2021-20308?: Integer overflow in the htmldoc 1.9.11 and before may allow attackers to execute arbitrary code and cause a denial of service that is similar to CVE-2017-9181.
How severe is CVE-2021-20308?: CVE-2021-20308 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-20308 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20308?: CVE-2021-20308 primarily affects Htmldoc Project Htmldoc. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-20308?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-20308 published?: CVE-2021-20308 was published on 2021-04-05 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:htmldoc_project:htmldoc:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

More vulnerabilities in Htmldoc Project Htmldoc

CVE-2024-46478 — Critical (CVSS 9.8): HTMLDOC v1.9.18 contains a buffer overflow in parse_pre function,ps-pdf.cxx:5681.
CVE-2024-45508 — Critical (CVSS 9.8): HTMLDOC before 1.9.19 has an out-of-bounds write in parse_paragraph in ps-pdf.cxx because of an attempt to strip…
CVE-2021-23165 — Critical (CVSS 9.8): A flaw was found in htmldoc before v1.9.12. Heap buffer overflow in pspdf_prepare_outpages(), in ps-pdf.cxx may lead to…
CVE-2021-23158 — Critical (CVSS 9.8): A flaw was found in htmldoc in v1.9.12. Double-free in function pspdf_export(),in ps-pdf.cxx may result in a…
CVE-2021-34121 — High (CVSS 7.8): An Out of Bounds flaw was discovered in htmodoc 1.9.12 in function parse_tree() in toc.cxx, this possibly leads to…
CVE-2021-34119 — High (CVSS 7.8): A flaw was discovered in htmodoc 1.9.12 in function parse_paragraph in ps-pdf.cxx ,this flaw possibly allows possible…

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Other CWE-190 (Integer Overflow or Wraparound) vulnerabilities

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CVE-2013-2555 — Critical (CVSS 10.0): Integer overflow in Adobe Flash Player before 10.3.183.75 and 11.x before 11.7.700.169 on Windows and Mac OS X, before…

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