CVE-2026-86428
DoS in commonmark AttributesExtension via crafted Markdown causing CPU exhaustion
Is CVE-2026-86428 being exploited?
Not confirmed. CVE-2026-86428 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.28% probability of exploitation in the next 30 days.
How severe is CVE-2026-86428?
CVE-2026-86428 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-86428?
Yes. A fix has been recorded for CVE-2026-86428. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-86428 affect?
CVE-2026-86428 affects league/commonmark >=1.5.0 and <2.10.0, Applications using commonmark-based Markdown rendering. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-86428?
Upgrade to commonmark >=2.10.0; rate-limit/sandbox Markdown processing.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote denial of service: crafted Markdown with many distinct attributes triggers quadratic-time processing, exhausting CPU and blocking legitimate requests.
Patch when possible
- affected>= 1.5.0 and < 2.10.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.