Inefficient regular expression complexity in vLLM - #VU139884
Published: July 28, 2026
Vulnerability identifier: #VU139884
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-1333
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to inefficient regular expression complexity in the lm-format-enforcer structured output backend when compiling attacker-supplied regular expressions. A remote attacker can send a specially crafted request containing a catastrophic regular expression to cause a denial of service.
Exploitation requires the operator to have selected the lm-format-enforcer backend for structured outputs.
Affected software
vLLM
Remediation
Install security update from vendor's website.
vLLM - update to 0.25.0 rc1