FastChat has a Content Moderation Bypass via Arena Side-by-Side Views
A vulnerability was detected in lm-sys fastchat up to 0.2.36. Impacted is the function add_text of the component Arena Side-by-Side View Handler. The manipulation results in incorrect control flow. The attack can be launched remotely. The exploit is now public and may be used. The root cause was fixed in commit 34eca62 for gradio_block_arena_named.py, but three other files were missed.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | fschat | <= 0.2.36 | no fix |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-6608
- https://github.com/lm-sys/FastChat/issues/3834
- https://gist.github.com/YLChen-007/e45039d23e698222d887ee09735d9d36
- https://github.com/lm-sys/FastChat
- https://vuldb.com/submit/792228
- https://vuldb.com/vuln/358243
- https://vuldb.com/vuln/358243/cti
- https://pypi.org/project/fschat
- https://github.com/advisories/GHSA-f3q6-69f3-vwch
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-670- Platform
- Python (PyPI)
- Package
fschat- Disclosed
- 20.04.2026
- Updated
- 11.10.2026 14:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2485 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-f3q6-69f3-vwch - 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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