How severe is CVE-2026-86428?

CVE-2026-86428 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-2026-86428 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-2026-86428?

CVE-2026-86428 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-86428?

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-2026-86428 published?

CVE-2026-86428 was published on 2026-09-07 and last updated on 2026-09-09.

CVE-2026-86428

CVE-2026-86428 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: 2026-09-09

Description

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.

Frequently asked questions

What is CVE-2026-86428?: commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing legitimate requests from completing.
How severe is CVE-2026-86428?: CVE-2026-86428 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-2026-86428 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-2026-86428?: CVE-2026-86428 affects Thephpleague Commonmark. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-86428?: 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-2026-86428 published?: CVE-2026-86428 was published on 2026-09-07 and last updated on 2026-09-09.

References

Affected products (1)

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

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