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Medium, CVSS 6.5amended

vLLM vulnerable to DoS via large Chat Completion or Tokenization requests with specially crafted chat_template_kwargs

CVE-2025-62426GHSA-69j4-grxj-j64p

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (vllm 0.11.1), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI vllm

    Affected
    >= 0.5.5, < 0.11.1
    Fixed in
    0.11.1

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.5 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2025-62426: 0.54% estimated exploitation activity in the next 30 days; percentile 45.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The /v1/chat/completions and /tokenize endpoints allow a chattemplatekwargs request parameter that is used in the code before it is properly validated against the chat template. With the right chattemplatekwargs parameters, it is possible to block processing of the API server for long periods of time, delaying all other requests Details In servingengine.py, the chattemplatekwargs are unpacked into kwargs passed to chatutils.py applyhfchattemplate with no validation on the keys or values in that chattemplatekwargs dict. This means they can be used to override optional parameters in the applyhfchattemplate method, such as tokenize, changing its default from False to True. https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/openai/servingengine.py#L809-L814 https://github.com/vllm-project/vllm/blob/2a6dc67eb520ddb9c4138d8b35ed6fe6226997fb/vllm/entrypoints/chatutils.py#L1602-L1610 Both servingchat.py and servingtokenization.py call…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-69j4-grxj-j64p

  2. Revision 1 · created ·

    Published from osv record GHSA-69j4-grxj-j64p

Agent brief

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# Patch Next advisory brief: CVE-2025-62426

Advisory: vLLM vulnerable to DoS via large Chat Completion or Tokenization requests with specially crafted `chat_template_kwargs`
IDs: CVE-2025-62426, GHSA-69j4-grxj-j64p
Record: https://patchnext.com/advisories/cve-2025-62426 (revision 2, source checked 26 Oct 2026, 13:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: vllm 0.11.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI vllm: affected >= 0.5.5, < 0.11.1; fixed in 0.11.1

## Suggested inspection (read-only)
- `python -m pip show vllm`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on vllm.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-69j4-grxj-j64p (OSV record GHSA-69j4-grxj-j64p lists affected ranges: PyPI vllm >=0.5.5 <0.11.1 (fixed))
- Verified: https://github.com/advisories/GHSA-69j4-grxj-j64p (GitHub-reviewed advisory GHSA-69j4-grxj-j64p lists affected ranges: PyPI vllm >=0.5.5 <0.11.1)

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