# CVE-2026-55574: vLLM: ReDoS via structured_outputs.regex compiled without timeout in xgrammar and outlines backends

> Attackers can cause denial of service in vLLM by submitting adversarial regular expressions that hang inference workers due to missing compilation timeouts.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Jul 2026
- **Updated:** 6 Jul 2026
- **Also known as:** GHSA-rwxx-mrjm-wc2m, MINI-3j92-96r2-cxwv, MINI-4m6m-jpm9-4v27, MINI-wqf2-7389-p943, PYSEC-2026-2304

## What is CVE-2026-55574?

CVE-2026-55574 is a high-severity denial of service vulnerability in Vllm Vllm, published on 6 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

vLLM is a high-throughput and memory-efficient inference and serving engine for LLMs. Prior to 0.24.0, the structured_outputs.regex API parameter passes a user-supplied regular expression string directly to the grammar compiler backends with no compilation timeout; in the xgrammar backend the string reaches the regex compiler with no guard, and in the outlines backend the validation step blocks structural issues such as lookarounds and backreferences but performs no complexity analysis, so a pattern with nested quantifiers passes all checks and causes exponential state-space expansion, allowing a single request containing an adversarial regex to hang an inference worker indefinitely and deny service. This issue is fixed in version 0.24.0.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-55574?

3 open source packages ship an affected version, including vllm. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `vllm` | PyPI | All versions | 0.24.0 |
| `vllm` | PyPI | All versions | 0.24.0 |
| `vllm` | PyPI | All versions | 0.24.0 |

Products: Vllm Vllm.

## How do I fix CVE-2026-55574?

Upgrade vllm to 0.24.0 or later.

## Is CVE-2026-55574 being exploited?

There is no known exploitation of CVE-2026-55574 in the wild and no public exploit code.

## Other vulnerabilities in Vllm Vllm

- [CVE-2025-32444](https://insights.sbomify.com/CVE-2025-32444/): vLLM Vulnerable to Remote Code Execution via Mooncake Integration (critical 10.0)
- [CVE-2026-22778](https://insights.sbomify.com/CVE-2026-22778/): vLLM leaks a heap address when PIL throws an error (critical 9.8)
- [CVE-2025-47277](https://insights.sbomify.com/CVE-2025-47277/): vLLM Allows Remote Code Execution via PyNcclPipe Communication Service (critical 9.8)
- [CVE-2024-11041](https://insights.sbomify.com/CVE-2024-11041/): Remote Code Execution in vllm-project/vllm (critical 9.8)
- [CVE-2026-48746](https://insights.sbomify.com/CVE-2026-48746/): vLLM: OpenAI auth bypass (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55574 and fix it if it is affected.

What it is: CVE-2026-55574 is a high-severity denial of service vulnerability in Vllm Vllm, published on 6 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55574 in the wild and no public exploit code.

Affected packages and fixed versions:
- vllm (PyPI): affected all versions; fixed in 0.24.0
- vllm (PyPI): affected all versions; fixed in 0.24.0
- vllm (PyPI): affected all versions; fixed in 0.24.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55574/ (Markdown: https://insights.sbomify.com/CVE-2026-55574/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55574
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55574
- OSV: https://osv.dev/vulnerability/CVE-2026-55574

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55574/
Summaries are generated and may contain mistakes; the official description above is the record.