How severe is CVE-2026-86430?

CVE-2026-86430 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-86430 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-86430?

CVE-2026-86430 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-86430?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-86430 published?

CVE-2026-86430 was published on 2026-09-07 and last updated on 2026-09-10.

CVE-2026-86430

CVE-2026-86430 is a high-severity vulnerability in Thephpleague Commonmark with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-407.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-407
Affected product: Thephpleague Commonmark
Published: 2026-09-07
Last modified: 2026-09-10

Description

league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent legitimate requests from completing.

Frequently asked questions

What is CVE-2026-86430?: league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent legitimate requests from completing.
How severe is CVE-2026-86430?: CVE-2026-86430 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-86430 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-86430?: CVE-2026-86430 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-86430?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-86430 published?: CVE-2026-86430 was published on 2026-09-07 and last updated on 2026-09-10.

References

Affected products (1)

cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:*

More vulnerabilities in Thephpleague Commonmark

CVE-2026-86429 — High (CVSS 7.5): The league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing…
CVE-2026-86428 — High (CVSS 7.5): commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when…
CVE-2026-86431 — High (CVSS 7.2): league/commonmark (thephpleague/commonmark) versions >= 2.7.0 and < 2.9.1 contain a cross-site scripting vulnerability…
CVE-2026-33347 — Medium (CVSS 6.1): league/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in…
CVE-2026-30838 — Medium (CVSS 6.1): league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by…
CVE-2019-10010 — Medium (CVSS 6.1): Cross-site scripting (XSS) vulnerability in the PHP League CommonMark library before 0.18.3 allows remote attackers to…

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