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CVE-2026-86433· NVD / CVE Program· CNA VulnCheck

commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes

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.

HighCVSS 8.7 · v4.0—No exploit Fix available
Published
Sep 7, 2026
Updated
Sep 8, 2026
EPSS
0.5% · 41th percentile
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Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · VulnCheck
8.7
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (VulnCheck). Independent of NVD's CPE analysis and usually ahead of it.

  • thephpleague commonmark

    • 2.8.4not affected
    • 1.5.0 and later · before 2.8.4affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12php-league-commonmarkall versions—
Debian:14php-league-commonmarkbefore 2.9.0-12.9.0-1

Same product

thephpleague: all records

Other highest-scoring records for the same primary product.

  • CVE-2024-58382league/commonmark before 2.6.0 Denial of Service via Quadratic Complexity
    34Monitor
  • CVE-2026-86435commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote
    34Monitor
  • CVE-2026-86434commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
    34Monitor
  • CVE-2026-86430league/commonmark before 2.9.1 Denial of Service via parsing
    34Monitor
  • CVE-2026-86429commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes
    34Monitor
  • CVE-2026-86428commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes
    34Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
thephpleague commonmark2.8.4Vendor (CNA)
debian:php-league-commonmark2.9.0-1 · Debian:14Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-864280 days apartcommonmark 1.5.0 before 2.10.0 Denial of Service via Attributes
    34Monitor
  • CVE-2026-864290 days apartcommonmark before 2.9.1 Denial of Service via SmartPunct and Attributes
    34Monitor
  • CVE-2026-864300 days apartleague/commonmark before 2.9.1 Denial of Service via parsing
    34Monitor
  • CVE-2026-864340 days apartcommonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
    34Monitor
  • CVE-2026-864350 days apartcommonmark 1.5.0 before 2.8.4 Denial of Service via Footnote
    34Monitor
  • CVE-2024-583822 days apartleague/commonmark before 2.6.0 Denial of Service via Quadratic Complexity
    34Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-407 · Inefficient Algorithmic Complexity

CVSS vector

CVSS: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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

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Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records