EM-20261103-1AYV VulnerabilityHigh severity

Mistune Vulnerability (CVE-2026-121437)

CVE-2026-121437

Status

Developing

Since Nov 03 15:17 UTC: signals keep joining.

First Signal: Nov 03 14:28 UTCC41 Red Hat Security Data
Page Born: Nov 03 15:17 UTCsecond source joined
Last Signal: Nov 03 15:17 UTC26 hours before snapshot
Sources: 21 official · 1 research, news or crowd
Open For: 24 hoursso far

Life Of This Page

1
Born

Nov 03 15:17 UTC
A second, independent source names it.
2
Developing · Now

Nov 03 15:17 UTC
New signals join; severity can move.
3
Confirmed

Not yet
CISA KEV lists it, or exploitation in the wild is reported.
4
Resolved

Not yet
Past the fix deadline and 14 days with no new signal.
5
Archived

Not yet
30 days after resolved. Read only; the link keeps working. Reopens if it comes back.

The address and ID never change. A correction is logged, never overwritten. If two pages turn out to be one incident, the later one points to the earlier.

Vulnerability Lifecycle

Disclosed: reached

Nov 03 15:17 UTC
C6 NVD published
Scored: reached

Nov 03 15:17 UTC
CVSS 8.7 · EPSS 0.6%
Exploited: not yet

Not yet
No exploitation reported
Advisories: not yet

Not yet
None yet
Vendor Response: reached

Nov 03 14:28 UTC
C41 published
Resolved: not yet

Not yet
After 14 quiet days

Timeline

Point at a mark to read it. Squares are signals, colored by severity; every one is also listed under Signals.

Signals

Nov 03 15:17 UTCCVE-2026-121437 (CVSS 8.7) (opens source in a new tab) Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU through quadratic-time emphasis delimiter processing. Attackers can submit small markdown documents w… High severityDatabaseC6 NVD CVE API 2.0
Nov 03 14:28 UTCRed Hat: CVE-2026-121437 (important) (opens source in a new tab) mistune: mistune: Denial of Service via quadratic-time emphasis delimiter processing High severityVendorC41 Red Hat Security Data