CVE-2026-6608

MediumCVSS 5.3

Published: 20/04/2026(UTC)Updated: 26/10/2026(UTC)Translated: 27/10/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.31%

23th percentile - higher than 23% of all known CVEs

Summary

A vulnerability in lm-sys fastchat up to 0.2.36 affects the add_text function in the Arena Side-by-Side View Handler component. Manipulation leads to incorrect control flow. The attack can be performed remotely, and the exploit is publicly available. The root cause was fixed in commit 34eca62 for gradio_block_arena_named.py, but three other files were missed.

Risk Assessment

An attacker can remotely exploit incorrect control flow, potentially leading to unexpected application behavior or security bypass. The public exploit increases the risk.

Recommendation

Update fastchat to a version containing the fix covering all affected files (not just gradio_block_arena_named.py). Until updated, restrict access to the Arena Side-by-Side interface.

Other vulnerabilities in fastchat

CVE-2026-85695Critical
FastChat contains an authentication bypass vulnerability in the /register_worker endpoint that allows unauthenticated attackers to register arbitrary worker addresses and perform server-side request forgery. Attackers can register malicious workers under victim model names to intercept user prompts, images, and responses, or probe internal network ports.

Original NVD description (English source)

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.

Vulnerability data from NVD (NIST) · CISA KEV · EPSS