# CVE-2025-32381: mlc-ai xgrammar unbounded memory cache denial of service

Source: https://junglewise.ai/threats/cve-2025-32381-mlc-ai-xgrammar-unbounded-memory-cache-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-04-09. Updated: 2026-06-08  
License: CC BY 4.0 with a link back

CVE-2025-32381 · Severity: medium · CVSS 6.5 · Published 2025-04-09

Xgrammar, a library used to speed up Large Language Model (LLM) operations, contains a flaw where it stores processed data in a memory cache without any size limits. An attacker can exploit this by sending a large number of unique requests, eventually consuming all available system memory. This results in a denial-of-service (DoS) condition, causing the AI service to crash or become unresponsive.

Technologies: [xgrammar (PyPI)](https://junglewise.ai/threats/technologies/xgrammar). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2025-32381 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-32381 being exploited in the wild.

**How severe is CVE-2025-32381?** Medium severity, with a CVSS score of 6.5, published 9 April 2025.

**Which products and versions are affected?** xgrammar (PyPI) < 0.1.18, ECOSYSTEM:introduced=0,fixed=0.1.18.

**Is there a fix for CVE-2025-32381?** Yes. xgrammar (PyPI): upgrade to 0.1.18 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-32381 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2025-32381?** Check whether you run xgrammar (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- xgrammar (PyPI): upgrade to 0.1.18 or later

  ```sh
  pip install "xgrammar>=0.1.18"
  ```


## Technical details

Xgrammar (prior to version 0.1.18) implements an unbounded in-memory cache for compiled grammars to improve performance. This component lacks resource limits (CWE-770), allowing an authenticated network attacker to trigger continuous memory allocation by providing unique inputs, such as distinct JSON schemas in LLM inference requests. This leads to memory exhaustion and a Denial of Service (DoS) of the host system. The vulnerability is mitigated in version 0.1.18 by introducing a configurable cache size limit.

## Affected products

- mlc-ai xgrammar < 0.1.18

## Identifiers

- CVE-2025-32381
- GHSA-389x-67px-mjg3
- PYSEC-2025-235

## Timeline

- 2025-04-08: disclosed: Initial disclosure to mlc-ai/xgrammar
- 2025-04-09: advisory: GitHub Advisory published
- 2025-04-09: patched: Version 0.1.18 released with cache limits

## References

- [https://api.github.com/users/russellb](https://api.github.com/users/russellb)
- [https://github.com/russellb](https://github.com/russellb)
- [https://api.github.com/users/russellb/gists%7B/gist_id%7D](https://api.github.com/users/russellb/gists%7B/gist_id%7D)
- [https://api.github.com/users/russellb/repos](https://api.github.com/users/russellb/repos)
- [https://avatars.githubusercontent.com/u/309258?v=4](https://avatars.githubusercontent.com/u/309258?v=4)
- [https://api.github.com/users/russellb/events%7B/privacy%7D](https://api.github.com/users/russellb/events%7B/privacy%7D)

## Related threats

- [PYSEC-2026-2055 - xgrammar vulnerable to denial of service by huge enum grammar](https://junglewise.ai/threats/cve-2025-58446-xgrammar-vulnerable-to-denial-of-service-by-huge-enum-grammar)
- [PYSEC-2026-2054 - XGrammar affected by Denial of Service by infinite recursion grammars](https://junglewise.ai/threats/cve-2025-57809-xgrammar-affected-by-denial-of-service-by-infinite-recursion)
- [mlc-ai xgrammar uncontrolled recursion in nested syntax](https://junglewise.ai/threats/cve-2026-25048-mlc-ai-xgrammar-uncontrolled-recursion-in-nested-syntax)