CVE-2026-59922: Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert)
CSIRTS triage
- What
- Quadratic-time parsing can occur on long runs of specific markers.
- Who is affected
- Users of Mistune plugins/formatting are affected.
- Urgency
- Remediation is urgent due to the high severity and potential for denial of service.
- Action
- Update Mistune to the latest version.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-59922
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-599220.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 29% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-59922 | coverage & exploitation status | NVD · CVE.org |
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