vllm-project vLLM up to 0.31.x Chat Template Rendering tokenizer.apply_chat_template iteration

Summaryinfo

A vulnerability has been found in vllm-project vLLM up to 0.31.x and classified as critical. Impacted is the function tokenizer.apply_chat_template of the component Chat Template Rendering. This manipulation causes iteration. This vulnerability is handled as CVE-2026-115911. The attack can be initiated remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability has been found in vllm-project vLLM up to 0.31.x and classified as critical. Affected by this vulnerability is the function tokenizer.apply_chat_template of the component Chat Template Rendering. The manipulation with an unknown input leads to a iteration vulnerability. The CWE definition for the vulnerability is CWE-834. The product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed. As an impact it is known to affect availability. The summary by CVE is:

vLLM is an inference and serving engine for large language models. From 0.19.0 until 0.32.0, authenticated callers can supply a request chat template when no server-side --chat-template is configured, or a malicious model repository can provide a template that is compiled and rendered by tokenizer.apply_chat_template() without a wall-clock timeout, output-size limit, or iteration bound. Rendering runs in a ThreadPoolExecutor with one worker by default, so a nonterminating render can block /v1/responses and other chat-template users after the request ends, while an output-expanding render can exhaust server memory. Harmony models are not affected because they do not use this Jinja path. This issue is fixed in version 0.32.0.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-115911 since 10/23/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 0.32.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• vllm-project

Name

• vLLM

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9
• 0.10
• 0.11
• 0.12
• 0.13
• 0.14
• 0.15
• 0.16
• 0.17
• 0.18
• 0.19
• 0.20
• 0.21
• 0.22
• 0.23
• 0.24
• 0.25
• 0.26
• 0.27
• 0.28
• 0.29
• 0.30
• 0.31

Website

• Product: https://github.com/vllm-project/vllm/

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