CVE-2026-86433

HIGH

7.5

CVSS v3

Description

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the Attributes extension where AttributesListener::findTargetAndDirection() performs quadratic-time sibling list scanning. Unauthenticated attackers can submit approximately 32 KB of repeated attribute blocks to cause parsing to take over 5 seconds, exhausting server resources.

CWE-407

How to fix

Remediation Available

php-league-commonmarkDebian

Fixed in:2.9.0-1CVE-2026-86433

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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityHigh

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

Exploit Intelligence

0.29%probability of exploitation in 30 days

22ndpercentile

Low risk: more likely to be exploited than 22% of all known CVEs.

References

Other references2

Related Vulnerabilities

Other CWE-407 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2020-27223	Medium	5.2	78%	-	Fix
CVE-2022-36021	Medium	5.5	61%	-	Fix
CVE-2021-33582	High	7.5	3.1%	-	Fix
CVE-2024-43485	High	7.5	3.1%	-	Fix
CVE-2024-43484	High	7.5	2.9%	-	Fix
CVE-2016-10396	High	7.5	2.9%	-	-

Common questions

How do I fix CVE-2026-86433?

Upgrade php-league-commonmark on debian unstable to 2.9.0-1 or later.

Is CVE-2026-86433 being actively exploited?

Not that we know of. CVE-2026-86433 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 22% of all scored CVEs.

How severe is CVE-2026-86433?

CVE-2026-86433 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-86433 affect?

Published advisories record a fix for php-league-commonmark (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2026-86433

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-09-08.