CVE-2026-86433

commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

8.7 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: None
Availability: High

Exploit likelihood

0.51%Up 0.2 points since Sep 8, 2026

What each source reports

CVE List Score used 8.7

commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

Record: CVE-2026-86433
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-407
Updated: 2026-11-02

EUVDEUVD-2026-72391 8.7

Record: EUVD-2026-72391
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-f9pm-gcpp-fwjp 8.7

commonmark versions from 1.5.0 before 2.8.4 contain a denial of service vulnerability in the...

Record: GHSA-f9pm-gcpp-fwjp
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-407
Updated: 2026-11-02

NVD 8.7

Record: CVE-2026-86433
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness: CWE-407
Updated: 2026-11-02

OSVDEBIAN-CVE-2026-86433 8.7

Record: DEBIAN-CVE-2026-86433
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Updated: 2026-11-02

OSVUBUNTU-CVE-2026-86433 8.7

Record: UBUNTU-CVE-2026-86433
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

Affected products

thephpleague commonmark

Affected packages

Affected packages
Package	Affected	Fixed
`php-league-commonmark` Debian:12	All versions, plus listed versions 2.10.0-12.10.1-12.10.3-12.3.9-12.3.9-1+deb12u1 Show 20 moreShow less 2.4.0-12.4.1-12.4.2-12.4.2-22.5.0-12.5.1-12.5.3-12.6.0-12.6.1-12.6.1-22.6.2-12.7.0-12.7.1-12.7.1-22.8.0-12.8.1-12.8.2-12.8.2-22.8.3-12.9.0-1	None known
`php-league-commonmark` Debian:13	All versions, plus listed versions 2.10.0-12.10.1-12.10.3-12.7.0-12.7.0-1+deb13u1 Show 8 moreShow less 2.7.1-12.7.1-22.8.0-12.8.1-12.8.2-12.8.2-22.8.3-12.9.0-1	None known
`php-league-commonmark` Debian:14	before 2.9.0-1, plus listed versions 2.7.0-12.7.1-12.7.1-22.8.0-12.8.1-12.8.2-12.8.2-22.8.3-1	2.9.0-1
`php-league-commonmark` Ubuntu:Pro:20.04:LTS	All versions, plus listed versions 1.1.2-11.2.0-11.3.0-11.3.1-11.3.1-1ubuntu21.3.1-1ubuntu2+esm1	None known
`php-league-commonmark` Ubuntu:Pro:22.04:LTS	All versions, plus listed versions 1.5.7-2build11.6.6-1build11.6.7-11.6.7-1ubuntu0.1~esm1	None known
`php-league-commonmark` Ubuntu:Pro:24.04:LTS	All versions, plus listed versions 2.3.9-12.4.1-12.4.2-12.4.2-22.4.2-2ubuntu0.1~esm1	None known
`php-league-commonmark` Ubuntu:26.04:LTS	All versions, plus listed versions 2.7.0-12.7.1-22.8.0-1	None known

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-86433 is a high vulnerability (CVSS 8.7) in Thephpleague Commonmark, published September 7, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.51%, the 43rd percentile. Fixed in php-league-commonmark 2.9.0-1.