CVE-2026-115916
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Off-by-One Error in vLLM Tokenizer Validation

Vulnerability report for CVE-2026-115916, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.

Publication date: 2026-10-26

Last updated on: 2026-10-26

Assigner: GitHub, Inc.

Description

vLLM is an inference and serving engine for large language models. Prior to 0.32.0, vllm/tokenizers/hf.py computes max_token_id with an off-by-one upper bound, allowing a pre-tokenized prompt ID equal to the vocabulary size to pass validation. For a tensor-parallel size of one and an exact multiple-of-64 vocabulary, VocabParallelEmbedding.forward does not mask that value before F.embedding uses it, causing a CUDA device-side assertion and terminating the engine. This issue is fixed in version 0.32.0.

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Meta Information

Published
2026-10-26
Last Modified
2026-10-26
Generated
2026-10-26
AI Q&A
2026-10-26
EPSS Evaluated
N/A
NVD
EUVD

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
vllm-project vllm < 0.32.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-193 A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
CWE-129 The product uses untrusted input when calculating or using an array index, but the product does not validate or incorrectly validates the index to ensure the index references a valid position within the array.

Attack-Flow Graph

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Executive Summary

vLLM versions before 0.32.0 have an off-by-one error in calculating max_token_id in vllm/tokenizers/hf.py. This allows a pre-tokenized prompt ID equal to the vocabulary size to pass validation. When tensor-parallel size is one and vocabulary size is a multiple of 64, VocabParallelEmbedding.forward fails to mask this value before F.embedding uses it, causing a CUDA device-side assertion that terminates the engine.

Detection Guidance

This vulnerability is specific to vLLM versions prior to 0.32.0 and involves a CUDA device-side assertion failure due to improper handling of token IDs. Detection requires checking the installed vLLM version and inspecting configurations where tensor-parallel size is one and vocabulary size is a multiple of 64.

Impact Analysis

This vulnerability can cause unexpected engine termination when processing specific inputs, leading to service disruption. It may result in denial of service for applications relying on vLLM for language model inference.

Mitigation Strategies

Upgrade vLLM to version 0.32.0 or later to address the off-by-one error and prevent the CUDA assertion failure. No additional commands are required beyond updating the software.

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