# CVE-2026-6607: FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426)

Source: https://junglewise.ai/threats/cve-2026-6607-fastchat-has-denial-of-service-through-blocking-event-loop-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-20. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-6607 · Severity: medium · CVSS 5.3 · Published 2026-04-20

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.

Technologies: [fschat (PyPI)](https://junglewise.ai/threats/technologies/fschat). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-6607 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-6607 being exploited in the wild.

**How severe is CVE-2026-6607?** Medium severity, with a CVSS score of 5.3, published 20 April 2026.

**Which products and versions are affected?** fschat (PyPI) <= 0.2.26, ECOSYSTEM:introduced=0,last_affected=0.2.26.

**Is there a fix for CVE-2026-6607?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**Am I affected by CVE-2026-6607?** Check whether you run fschat (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Affected products

- fschat (PyPI) <= 0.2.26, ECOSYSTEM:introduced=0,last_affected=0.2.26

## Identifiers

- CVE-2026-6607
- GHSA-5h65-jx66-j7p5
- PYSEC-2026-2484

## References

- [https://github.com/lm-sys/FastChat/issues/3833](https://github.com/lm-sys/FastChat/issues/3833)
- [https://github.com/lm-sys/FastChat/pull/3835](https://github.com/lm-sys/FastChat/pull/3835)
- [https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33](https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33)
- [https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5](https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5)
- [https://github.com/lm-sys/FastChat](https://github.com/lm-sys/FastChat)

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