CVE-2026-86434

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Source
https://cve.org/CVERecord?id=CVE-2026-86434
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-86434.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-86434
Aliases
Downstream
Published
2026-09-07T12:53:53Z
Modified
2026-10-20T12:02:32Z
Severity
  • 8.7 (High) CVSS_V4 - 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 CVSS Calculator
Summary
commonmark 2.0.0 through 2.8.3 Denial of Service via Slug Collision
Details

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.

Database specific 
{
    "cna_assigner":  "VulnCheck",
    "cwe_ids":  [
        "CWE-407"
    ],
    "osv_generated_from":  "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86434.json",
    "unresolved_ranges":  [
        {
            "extracted_events":  [
                {
                    "introduced":  "2.0.0"
                },
                {
                    "fixed":  "2.8.4"
                }
            ],
            "source":  "AFFECTED_FIELD"
        },
        {
            "extracted_events":  [
                {
                    "introduced":  "2.0.0"
                },
                {
                    "fixed":  "2.8.4"
                }
            ],
            "source":  "CPE_FIELD"
        }
    ]
}
References

Affected packages

Git / github.com/thephpleague/commonmark

Affected ranges

Type
GIT
Repo
https://github.com/thephpleague/commonmark
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
5703d83ba3da3b2e356a5fedc848ed6d8ffb6529
Database specific
Show details 
{
    "extracted_events":  [
        {
            "range":  [
                {
                    "introduced":  "0"
                },
                {
                    "fixed":  "2.9.0"
                }
            ],
            "source":  "DESCRIPTION"
        }
    ]
}

Affected versions

0.*
0.1.0
0.1.1
0.1.2
0.10.0
0.11.0
0.11.1
0.11.2
0.11.3
0.12.0
0.13.0
0.13.1
0.13.2
0.13.3
0.13.4
0.14.0
0.15.0
0.15.1
0.15.2
0.15.3
0.15.4
0.15.5
0.15.6
0.15.7
0.16.0
0.17.0
0.17.2
0.17.4
0.18.1
0.2.0
0.2.1
0.3.0
0.4.0
0.5.0
0.5.1
0.6.0
0.6.1
0.7.0
0.7.1
0.8.0
0.9.0
2.*
2.0.0
2.0.0-beta1
2.0.0-beta2
2.0.0-beta3
2.0.0-rc1
2.0.0-rc2
2.0.1
2.0.2
2.1.0
2.2.0
2.3.0
2.4.0
2.5.0
2.6.0
2.7.0
2.8.0

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-86434.json"