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CVE-2026-6608: lm-sys fastchat Arena Side-by-Side View add_text control flow

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-20 · updated 2026-10-26
• Weakness: CWE-670

Description

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 products

• lm-sys/fastchat: 0.2.0, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.2.5 (+31)

References

• https://gist.github.com/YLChen-007/e45039d23e698222d887ee09735d9d36
• https://github.com/lm-sys/FastChat/
• https://github.com/lm-sys/FastChat/issues/3834
• https://vuldb.com/submit/792228
• https://vuldb.com/vuln/358243
• https://vuldb.com/vuln/358243/cti

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