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CVE-2026-86434: commonmark 2.0.0 to before 2.8.4
CVE-2026-86434. CVSS 3.1 base score 7.5 (HIGH, Vendor/CNA). EPSS 0.00509 (percentile 0.41482), scored 2026-10-06.
Affected technology
commonmark · 2.0.0 to before 2.8.4
thephpleague
Description’s affected range: versions >= 2.0.0 and < 2.8.4 (patched in 2.9.0)
Component: Not specified by the source
Attack conditions (Vendor/CNA, CVSS 4.0): Network (remote) · No privileges required · No user interaction required
What an attacker can do
An unauthenticated attacker can force many headings onto a single base slug (e.g., via empty ATX headings, identical heading text, or punctuation-only headings) in a small Markdown document, consuming excessive CPU and denying service. Vendor/CNA’s CVSS 4.0 assessment (base score 8.7/10) rates confidentiality and integrity impact as none; availability impact as high.
- CWE
- CWE-407
- CCR priority
- 30.1 /100 (P4)
- CVSS 3.1
- 7.5 /10 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H · Vendor/CNA
- EPSS
- 0.00509 · percentile 0.41593 · 2026-10-08
- KEV
- no
Provenance
- FIRST EPSS daily exploit-probability · Source record · observed 2026-10-08 17:36:22.845483+00:00 UTC
- NVD CVE API 2.0 · Source record · observed 2026-10-08 17:32:11.049884+00:00 UTC
Stable permalink: https://cybercodered.org/item/cve-cve-2026-86434.html