# CVE-2026-6607: lm-sys fastchat Worker API Endpoint api_generate resource consumption

> Remote attackers can cause resource exhaustion in the fastchat Worker API, leading to denial of service.

- **Severity:** Medium 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/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-5h65-jx66-j7p5, PYSEC-2026-2484

## What is CVE-2026-6607?

CVE-2026-6607 is a medium-severity denial of service vulnerability in lm-sys fastchat, published on 20 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A security vulnerability has been detected in lm-sys fastchat up to 0.2.36. This issue affects the function api_generate of the component Worker API Endpoint. The manipulation leads to resource consumption. The attack can be initiated remotely. The exploit has been disclosed publicly and may be used. The identifier of the patch is c9e84b89c91d45191dc24466888de526fa04cf33. It is suggested to install a patch to address this issue. Commit ff66426 patched this issue in api_generate of base_model_worker.py and did miss other entry points.

Weakness: CWE-404 (Improper Resource Shutdown or Release), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-6607?

3 open source packages ship an affected version, including fschat.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fschat` | PyPI | All versions to 0.2.26 | None |
| `fschat` | PyPI | All versions to 0.2.26 | None |
| `fschat` | PyPI | All versions to 0.2.26 | None |

## How do I fix CVE-2026-6607?

No fix has been published for CVE-2026-6607 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6607 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6607 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6607 and fix it if it is affected.

What it is: CVE-2026-6607 is a medium-severity denial of service vulnerability in lm-sys fastchat, published on 20 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6607 exists.

Affected packages and fixed versions:
- fschat (PyPI): affected all versions up to 0.2.26; no fix listed
- fschat (PyPI): affected all versions up to 0.2.26; no fix listed
- fschat (PyPI): affected all versions up to 0.2.26; no fix listed

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-2026-6607/ (Markdown: https://insights.sbomify.com/CVE-2026-6607/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6607
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6607
- OSV: https://osv.dev/vulnerability/CVE-2026-6607

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6607/
Summaries are generated and may contain mistakes; the official description above is the record.