CVE-2026-34756
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network with a low-privilege account. High risk of service disruption.
- Exploit odds
- 0.4% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.4% in the next 30 days (EPSS).
- Severity: 6.5 MEDIUM (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.4% · EPSS, next 30 days
- Weakness
- CWE-770 · Allocation without limits
- Record status
- Modified
Affected
- Vllm < 0.19.0
Attack profile CVSS 3.1 · 6.5
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-34756.md and follow it. Check whether this project is affected by CVE-2026-34756. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380
- https://github.com/vllm-project/vllm/pull/37952
- https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528
References
- https://github.com/vllm-project/vllm/commit/b111f8a61f100fdca08706f41f29ef3548de7380
- https://github.com/vllm-project/vllm/pull/37952
- https://github.com/vllm-project/vllm/security/advisories/GHSA-3mwp-wvh9-7528
- https://access.redhat.com/errata/RHSA-2026:36005
- https://access.redhat.com/errata/RHSA-2026:36006
- https://access.redhat.com/errata/RHSA-2026:57380
- https://access.redhat.com/errata/RHSA-2026:57387
- https://access.redhat.com/errata/RHSA-2026:57389
- https://access.redhat.com/errata/RHSA-2026:57390
- https://access.redhat.com/errata/RHSA-2026:59144
- https://access.redhat.com/errata/RHSA-2026:59151
- https://access.redhat.com/security/cve/CVE-2026-34756
- https://bugzilla.redhat.com/show_bug.cgi?id=2455425
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34756.json