Exposure of Data Element to Wrong Session in vLLM - #VU165865
Published: November 11, 2026
Vulnerability identifier: #VU165865
CSH Severity: Low
CVSS v4: 6 [CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-488
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to disrupt another concurrent request's generation by forcing the configured reasoning-end sequence, such as </think>, into its output.
The vulnerability exists due to failure to remove source entries in the V1 model runner's ThinkingBudgetStateHolder.sync_batch() when swapping a budgeted row with an unbudgeted row, aliasing mutable state across requests. A remote user can submit a completion request with thinking_token_budget and groom the queue to trigger a mixed batch swap on a reasoning-enabled server to force the configured reasoning-end sequence into a victim's output.
Affected software
vLLM
Remediation
Install security update from vendor's website.
vLLM - update to 0.28.0