FastChat Uncontrolled Resource Consumption vulnerability
In lm-sys/fastchat Release v0.2.36, the server fails to handle excessive characters appended to the end of multipart boundaries. This flaw can be exploited by sending malformed multipart requests with arbitrary characters at the end of the boundary. Each extra character is processed in an infinite loop, leading to excessive resource consumption and a complete denial of service (DoS) for all users. The vulnerability is unauthenticated, meaning no user login or interaction is required for an attacker to exploit this issue.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | fschat | <= 0.2.36 | no fix |
References
- CVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400, CWE-835- Platform
- Python (PyPI)
- Package
fschat- Disclosed
- 20.03.2025
- Updated
- 11.10.2026 13:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1398 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-qg86-f892-m4hj - 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 Uncontrolled Resource Consumption vulnerability this entry
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