What is CVE-2026-6608?

CVE-2026-6608 is a medium-severity vulnerability in Lm-Sys Fastchat, classified under Always-Incorrect Control Flow Implementation. CVSS score: 5.3/10. Published 2026-04-20.

How severe is CVE-2026-6608?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Lm-Sys Fastchat

CVE-2026-6608

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.

Published 2026-04-20 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.005 (41.2th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 41.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002

Affected products

Lm-Sys Fastchat — versions 0.2.0, 0.2.1, 0.2.2

Weakness classification (CWE)

CWE-670 — Always-Incorrect Control Flow Implementation

References

vuldb.com/vuln/358243 (technical-description, vdb-entry)
vuldb.com/vuln/358243/cti (signature, permissions-required)
vuldb.com/submit/792228 (third-party-advisory)
github.com/lm-sys/FastChat/issues/3834 (issue-tracking)
gist.github.com/YLChen-007/e45039d23e698222d887ee09735d9d36 (exploit)
github.com/lm-sys/FastChat/ (product)

Frequently asked questions

What is CVE-2026-6608?: CVE-2026-6608 is a medium-severity vulnerability in Lm-Sys Fastchat, classified under Always-Incorrect Control Flow Implementation. CVSS score: 5.3/10. Published 2026-04-20.
How severe is CVE-2026-6608?: Medium severity. CVSS v3 base score is 5.3 out of 10.