CVE-2026-121437: Mistune 3.3.0 before 3.3.4 Quadratic-Time DoS via _process_emphasis_delimiters
lepture · mistune
Fixed in 3.3.4 · Affected: lepture mistune before 3.3.4 · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 50% of scored CVEs
DescriptionCVE.org
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 with repeated patterns like "*a_b" to trigger an O(n²) index-fixup loop, stalling workers for seconds.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- lepture · mistunefrom 3.3.0 before 3.3.4
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Vendor
- lepture
- Published
- November 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-121437 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.