CVE-2026-115349 Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing
High 8.7
Published
Updated
Check this codebase for CVE-2026-115349 and fix it if it is affected.
What it is: CVE-2026-115349 is a high-severity vulnerability in lepture mistune, published on 22 Oct 2026.
Exploitation: There is no known exploitation of CVE-2026-115349 in the wild and no public exploit code.
Affected product: lepture mistune. No package-level version data is available, so check the vendor advisory linked from the reference page.
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2026-115349/ (Markdown: https://insights.sbomify.com/CVE-2026-115349/index.md)
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-115349?
CVE-2026-115349 is a high-severity vulnerability in lepture mistune, published on 22 Oct 2026.
Official description
Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.
Weakness: CWE-1333
Which versions are affected by CVE-2026-115349?
How do I fix CVE-2026-115349?
No fix has been published for CVE-2026-115349 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-115349 being exploited?
There is no known exploitation of CVE-2026-115349 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-115349, GHSA-3q64-rw38-243v, GHSA-4239-8pr8-4pwv, UBUNTU-CVE-2026-115349.