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CVE-2026-34756

🔶 medium
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Summary

vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memo

Description

vLLM is an inference and serving engine for large language models (LLMs). From 0.1.0 to before 0.19.0, a Denial of Service vulnerability exists in the vLLM OpenAI-compatible API server. Due to the lack of an upper bound validation on the n parameter in the ChatCompletionRequest and CompletionRequest Pydantic models, an unauthenticated attacker can send a single HTTP request with an astronomically large n value. This completely blocks the Python asyncio event loop and causes immediate Out-Of-Memory crashes by allocating millions of request object copies in the heap before the request even reaches the scheduling queue. This vulnerability is fixed in 0.19.0.

CVSS Score
6.5
Medium
EPSS Score
0.0
Exploit Probability
Published Date
2026-04-06
First Seen: 2026-04-07
📊 Relative Risk Intelligence

This CVE is Lower Risk - more severe than 47.8% of all 326,604 vulnerabilities in our database.

#170,379
Below average severity
Severity Percentile
🎯 CISA SSVC Assessment Updated: Apr 7, 2026
🔍 Exploitation Status
None
No known exploits
⚙️ Automatable
NO
Requires human interaction
💥 Technical Impact
Partial
Limited system impact
SSVC data provided by CISA
Last Modified 2026-04-20
Source NVD 🔗
CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE IDs (Weakness Types)
CWE-770

📦 Affected Products 1

Vendor Product Status Affected Versions
vllm vllm Affected
> 0.1.0 < 0.19.0

🔗 References 3

https://github.com/vllm-project/vllm/commit/b111f8a6...
Patch
https://github.com/vllm-project/vllm/pull/37952
Issue Tracking Patch
https://github.com/vllm-project/vllm/security/adviso...
Patch Vendor Advisory

🔗 Related CVEs 6

CVE ID Severity CVSS EPSS Summary Published
CVE-2026-44222 🔶 medium 6.5 0.0 vLLM is an inference and serving engine for large language models (LLMs). From 0.6.1 to before 0.20.0, there is a a Toke... 2026-05-12
CVE-2026-44223 🔶 medium 6.5 0.0 vLLM is an inference and serving engine for large language models (LLMs). From to before 0.20.0, the extract_hidden_sta... 2026-05-12
CVE-2026-7141 🔶 medium 5.6 0.1 A vulnerability was found in vllm up to 0.19.0. The affected element is the function has_mamba_layers of the file vllm/v... 2026-04-27
CVE-2026-34753 🔶 medium 5.4 0.0 vLLM is an inference and serving engine for large language models (LLMs). From 0.16.0 to before 0.19.0, a server-side re... 2026-04-06
CVE-2026-34755 🔶 medium 6.5 0.1 vLLM is an inference and serving engine for large language models (LLMs). From 0.7.0 to before 0.19.0, the VideoMediaIO.... 2026-04-06
CVE-2026-34760 🔶 medium 5.9 0.1 vLLM is an inference and serving engine for large language models (LLMs). From version 0.5.5 to before version 0.18.0, L... 2026-04-02
These CVEs affect the same products