CVE-2026-86434— commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
Quick assessment
Affected
thephpleague commonmark
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
The League of Extraordinary Packages league/commonmark是The League of Extraordinary Packages组织开源的一款Markdown解析组件。 The League of Extraordinary Packages league/commonmark 2.0.0至2.8.4之前版本存在资源管理错误漏洞，该漏洞源于UniqueSlugNormalizer::normalize()在每次slug冲突时从1重新开始数值后缀搜索，导
Possible ATT&CK Techniques 2 AI
T1059 · Command and Scripting Interpreter T1190 · Exploit Public-Facing ApplicationAffected Version Matrix 2
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| thephpleague | commonmark | 2.0.0< 2.8.4 |
affected |
2.8.4 |
unaffected |
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I. Basic Information for CVE-2026-86434
Vulnerability Information
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Vulnerability Title
commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
Source: CVE Program / CVE List V5
Vulnerability Description
league/commonmark versions >= 2.0.0 and < 2.8.4 (patched in 2.9.0) contain a denial of service vulnerability in UniqueSlugNormalizer::normalize(), which restarts its numeric-suffix search from 1 on every slug collision, resulting in O(K^2) time complexity for K headings that collapse to the same base slug. The vulnerable path is reached when HeadingPermalinkExtension, FootnoteExtension, or TableOfContentsExtension is registered. 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5
Vulnerability Title
The League of Extraordinary Packages league/commonmark 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
The League of Extraordinary Packages league/commonmark是The League of Extraordinary Packages组织开源的一款Markdown解析组件。 The League of Extraordinary Packages league/commonmark 2.0.0至2.8.4之前版本存在资源管理错误漏洞，该漏洞源于UniqueSlugNormalizer::normalize()在每次slug冲突时从1重新开始数值后缀搜索，导
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| thephpleague | commonmark | 2.0.0 ~ 2.8.4 | - |
|
II. Public POCs for CVE-2026-86434
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Advisories for CVE-2026-86434 (2)
Same Patch Batch · thephpleague · 2026-09-07 · 8 CVEs total
| CVE-2026-86430 | 7.5 HIGH | league/commonmark before 2.9.1 Denial of Service via parsing |
| CVE-2026-86429 | 7.5 HIGH | commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes |
| CVE-2026-86435 | 7.5 HIGH | commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote |
| CVE-2026-86433 | 7.5 HIGH | commonmark 1.5.0 before 2.8.4 Denial of Service via Attributes |
| CVE-2026-86428 | 7.5 HIGH | commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes |
| CVE-2026-86431 | 7.2 HIGH | commonmark before 2.9.1 XSS via AttributesExtension form feed bypass |
| CVE-2026-86432 | 5.3 MEDIUM | commonmark 2.0.0 before 2.8.4 Denial of Service via XML |
IV. Related Vulnerabilities
Same product: commonmark
-
CVE-2026-105830
league/commonmark 2.0.0 before 2.10.2 Quadratic DoS via Tabl -
CVE-2026-105829
League CommonMark 1.3.0 before 2.10.2 Stored XSS via Disallo -
CVE-2024-58382
league/commonmark before 2.6.0 Denial of Service via Quadrat -
CVE-2026-86435
commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote -
CVE-2026-86433
commonmark 1.5.0 before 2.8.4 Denial of Service via Attribut
Same vendor: thephpleague
-
CVE-2026-105830
league/commonmark 2.0.0 before 2.10.2 Quadratic DoS via Tabl -
CVE-2026-105829
League CommonMark 1.3.0 before 2.10.2 Stored XSS via Disallo -
CVE-2026-102601
Flysystem: WhitespacePathNormalizer's control-character (Cor -
CVE-2024-58382
league/commonmark before 2.6.0 Denial of Service via Quadrat -
CVE-2026-86435
commonmark 1.5.0 before 2.8.4 Denial of Service via Footnote
Same weakness: CWE-407
-
CVE-2026-16762
Denial-of-service vulnerability in the Qt Core QXmlStream pa -
CVE-2026-89314
Quadratic-time key_ops duplicate check lets a sub-1 MB JWKS -
CVE-2026-115352
Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Bracke -
CVE-2026-115347
Mistune before 3.3.0 Quadratic Denial of Service via parse_l -
CVE-2026-115319
fzf 0.36.0 through 0.74.5 Denial of Service via maskActionCo
V. Comments for CVE-2026-86434
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