FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426)
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 but missed other entry points.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | fschat | <= 0.2.26 | no fix |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-6607
- https://github.com/lm-sys/FastChat/issues/3833
- https://github.com/lm-sys/FastChat/pull/3835
- https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33
- https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5
- https://github.com/lm-sys/FastChat
- https://vuldb.com/submit/792227
- https://vuldb.com/vuln/358242
- https://vuldb.com/vuln/358242/cti
- https://pypi.org/project/fschat
- https://github.com/advisories/GHSA-5h65-jx66-j7p5
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness (CWE)
CWE-400- Platform
- Python (PyPI)
- Package
fschat- Disclosed
- 20.04.2026
- Updated
- 11.10.2026 14:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2484 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-5h65-jx66-j7p5 - CC BY 4.0
Vulnerability history: fschat
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 03.2025 04.2026
- Without a fix
- 7
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 3
Disclosures per year
- 2025: 5
- 2026: 2
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FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426) this entry
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