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Fencer Vulns
medium 5.3

CVE-2026-73556 json

vLLM: ReDoS via structured_outputs.regex in the lm-format-enforcer backend (no compile timeout) — missed sibling of CVE-2026-55574

published 2026-08-13 2 mo ago modified 2026-09-28 41 d ago also EUVD-2026-58063 , GHSA-48jh-3gj7-fg8v , PYSEC-2026-3933

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

vLLM is an inference and serving engine for large language models. Prior to 0.26.0, the structured_outputs.regex parameter in vllm/v1/structured_output/backend_lm_format_enforcer.py is passed to lmformatenforcer.RegexParser without compile_regex_with_timeout or validation in validate_structured_output_request_lm_format_enforcer, allowing an unauthenticated /v1/completions request against the lm-format-enforcer backend to consume a CPU core and stall the structured-output engine path with a catastrophic regular expression. This issue is fixed in version 0.26.0.

Patch / fix

  • pypi vllm 0.26.0
  • vllm-project vllm 0.26.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-73556 updated cvss 7.5

vllm: vLLM: Denial of Service via Regular Expression processing

  • Red Hat AI Inference Server rhaii/vllm-tpu-rhel9, rhaiis/vllm-cpu-rhel9, rhaiis/vllm-tpu-rhel9, rhaiis/vllm-rocm-rhel9, rhaii/vllm-neuron-rhel9, rhaiis/vllm-spyre-rhel9, +1 more
    affected: no fix available, no fix planned “Will not fix”
  • Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-gaudi-rhel9
    affected: no fix planned “Will not fix”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-llm-d-kv-cache-rhel9
    affected: no fix available, no fix planned “Will not fix”
  • Red Hat AI Inference Server 3.3 rhaiis/vllm-cuda-rhel9 1789582776
    fixed: vendor fix RHSA-2026:68699
  • Red Hat AI Inference Server 3.4 rhaii/vllm-cpu-rhel9 1789681128, rhaii/vllm-cpu-rhel9 1790075793, rhaii/vllm-cuda-rhel9 1789681126, rhaii/vllm-cuda-rhel9 1790090131, rhaii/vllm-rocm-rhel9 1789681126, rhaii/vllm-rocm-rhel9 1790109620, +2 more
    fixed: vendor fix RHSA-2026:69466
  • Red Hat AI Inference Server 3.5 rhaii/vllm-cpu-rhel9 1791473614, rhaii/vllm-cpu-rhel9 1793444554, rhaii/vllm-cuda-rhel9 1791473631, rhaii/vllm-cuda-rhel9 1793444600, rhaii/vllm-rocm-rhel9 1791425869, rhaii/vllm-rocm-rhel9 1793444456, +4 more
    fixed: vendor fix RHSA-2026:82415
  • Red Hat Enterprise Linux AI 3.3 rhelai3/bootc-cuda-rhel9 1790866732, rhelai3/bootc-aws-cuda-rhel9 1790936334, rhelai3/bootc-gcp-cuda-rhel9 1790936334, rhelai3/disk-image-cuda-rhel9 1790954179, rhelai3/bootc-azure-cuda-rhel9 1790936351
    fixed: vendor fix RHSA-2026:76041
  • Red Hat Enterprise Linux AI 3.4 rhelai3/bootc-cuda-rhel9 1790868254, rhelai3/bootc-rocm-rhel9 1790614447, rhelai3/bootc-aws-cuda-rhel9 1790881122, rhelai3/bootc-gcp-cuda-rhel9 1790881123, rhelai3/disk-image-cuda-rhel9 1790957417, rhelai3/bootc-azure-cuda-rhel9 1790881120, +1 more
    fixed: vendor fix RHSA-2026:76150
show 5 more
  • Red Hat Enterprise Linux AI 3.5 rhelai3/bootc-cuda-rhel9 1793135861, rhelai3/bootc-rocm-rhel9 1793135863, rhelai3/bootc-aws-cuda-rhel9 1793194817, rhelai3/bootc-gcp-cuda-rhel9 1793194815, rhelai3/disk-image-cuda-rhel9 1793206758, rhelai3/bootc-azure-cuda-rhel9 1793194815, +1 more
    fixed: vendor fix RHSA-2026:92452
  • Red Hat OpenShift AI 3.4 rhoai/odh-kserve-agent-rhel9 1791468381, rhoai/odh-kserve-router-rhel9 1791468401, rhoai/odh-kserve-controller-rhel9 1791468368, rhoai/odh-kserve-storage-initializer-rhel9 1790958549
    fixed: vendor fix RHSA-2026:84734
  • Red Hat Enterprise Linux AI 3.3 rhelai3/bootc-rocm-rhel9 1790791893, rhelai3/bootc-azure-rocm-rhel9 1790850900
    not affected: vulnerable code not present
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-th-torch-cuda-py312-rhel9
    not affected: vulnerable code not in execute path
  • Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1791509689, rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-trainer-rhel9 1791869783, +96 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/vllm-project/vllm/security/advisories/GHSA-48jh-3gj7-fg8v referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
pypi vllm
<0.26.0
0.26.0

Affected products

  • vllm-project vllm

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption
  • CWE-1333 Inefficient Regular Expression Complexity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.