CVE-2026-86429
Denial-of-service via quadratic Markdown parsing in league/commonmark (<2.9.1).
Is CVE-2026-86429 being exploited?
Not confirmed. CVE-2026-86429 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 0.29% probability of exploitation in the next 30 days.
How severe is CVE-2026-86429?
CVE-2026-86429 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-2026-86429?
Yes. A fix has been recorded for CVE-2026-86429. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-86429 affect?
CVE-2026-86429 affects thephpleague/commonmark >=1.5.0, <2.9.1, PHP applications that register SmartPunctExtension or AttributesExtension. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-86429?
Upgrade to commonmark 2.9.1 or disable SmartPunct/Attributes extensions until patched.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated attacker can send crafted Markdown to trigger quadratic CPU consumption in SmartPunct/Attributes extensions, causing high CPU and service outage (DoS).
Patch when possible
- affected>= 1.5.0 and < 2.9.1
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.