Is CVE-2026-34756 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-34756 being exploited in the wild.

How severe is CVE-2026-34756?

Medium severity, with a CVSS score of 6.5, published 6 April 2026.

Which products and versions are affected?

vllm (PyPI) ECOSYSTEM:introduced=0.1.0,fixed=0.19.0; Red Hat AI Inference Server 3.

Is there a fix for CVE-2026-34756?

Yes. vllm (PyPI): upgrade to 0.19.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-34756 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-34756?

Check whether you run vllm (PyPI), Red Hat AI Inference Server or Vllm 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.

CVE-2026-34756: vLLM Denial of Service via unbounded n parameter in OpenAI API server

CVE-2026-34756 · Severity: medium · CVSS 6.5 · Published 2026-04-06

vLLM is a high-throughput engine for serving AI models via an OpenAI-compatible interface. A vulnerability in how it handles certain request parameters allows an attacker to crash the server by sending a single specially crafted request. This results in a complete service outage, potentially impacting AI-powered applications and customer-facing services.

Technologies: vllm (PyPI), Red Hat AI Inference Server, Vllm. Vendors: PyPI, Red Hat, Vllm.

Quick answers

Is CVE-2026-34756 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-34756 being exploited in the wild.
How severe is CVE-2026-34756?: Medium severity, with a CVSS score of 6.5, published 6 April 2026.
Which products and versions are affected?: vllm (PyPI) ECOSYSTEM:introduced=0.1.0,fixed=0.19.0; Red Hat AI Inference Server 3.
Is there a fix for CVE-2026-34756?: Yes. vllm (PyPI): upgrade to 0.19.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-34756 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-34756?: Check whether you run vllm (PyPI), Red Hat AI Inference Server or Vllm 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

vllm (PyPI): upgrade to 0.19.0 or later
```
pip install "vllm>=0.19.0"
```

Technical details

A resource exhaustion vulnerability exists in vLLM's OpenAI-compatible API server due to missing upper-bound validation on the 'n' parameter in ChatCompletionRequest and CompletionRequest models. An attacker can provide an extremely large integer for 'n', which causes the server to enter a synchronous loop that clones the request object millions of times. This behavior monopolizes the Python asyncio event loop and rapidly consumes system memory (RSS), triggering the OS OOM-killer. The vulnerability is reachable via the network without authentication in default configurations. A fix is available in version 0.19.0.

Affected products

vllm-project vllm >= 0.1.0, < 0.19.0

Identifiers

CVE-2026-34756
GHSA-3mwp-wvh9-7528
PYSEC-2026-2298

Timeline

2026-04-03: disclosed
2026-04-03: advisory
2026-04-03: patched: Fixed in version 0.19.0

References

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