CVE-2026-93840: vLLM before 0.29.0 Cross-Request Logits Corruption via allowed_token_ids

Vulnerability summary

CVE-2026-93840 is a medium (CVSS 6.3) Improper Validation of Array Index vulnerability in vllm-project vllm. EPSS estimates a 0.25% chance of exploitation in the next 30 days, higher than 14.9% of scored vulnerabilities.

Timeline

1. 18-09-2026
   PublishedVulnerability first disclosed.
2. 24-09-2026
   Last modifiedVulnerability information updated.

Description

vLLM before 0.29.0 validates allowed_token_ids against tokenizer length instead of model output logits width in SamplingParams._validate_allowed_token_ids(). Attackers can supply token IDs above the output vocabulary that pass validation, causing LogitBiasState to corrupt GPU logits state and allow concurrent requests to sample tokens outside their allowlists.

• CWE-129Improper Validation of Array IndexThe 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.