CVE-2026-6608

lm-sys fastchat Arena Side-by-Side View add_text control flow

Published Apr 20, 2026 CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

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

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

lm-sys

fastchat

affected

Version	Status	Constraints
`0.2.0`	affected	—
`0.2.1`	affected	—
`0.2.2`	affected	—
`0.2.3`	affected	—
`0.2.4`	affected	—
`0.2.5`	affected	—
`0.2.6`	affected	—
`0.2.7`	affected	—
`0.2.8`	affected	—
`0.2.9`	affected	—
`0.2.10`	affected	—
`0.2.11`	affected	—
`0.2.12`	affected	—
`0.2.13`	affected	—
`0.2.14`	affected	—
`0.2.15`	affected	—
`0.2.16`	affected	—
`0.2.17`	affected	—
`0.2.18`	affected	—
`0.2.19`	affected	—
`0.2.20`	affected	—
`0.2.21`	affected	—
`0.2.22`	affected	—
`0.2.23`	affected	—
`0.2.24`	affected	—
`0.2.25`	affected	—
`0.2.26`	affected	—
`0.2.27`	affected	—
`0.2.28`	affected	—
`0.2.29`	affected	—
`0.2.30`	affected	—
`0.2.31`	affected	—
`0.2.32`	affected	—
`0.2.33`	affected	—
`0.2.34`	affected	—
`0.2.35`	affected	—
`0.2.36`	affected	—

No data.

Vendor Product Versions

Lm-sys

Fastchat

Version	Status	Scheme	Platform
`0.2.0`	affected	semver	—
`0.2.1`	affected	semver	—
`0.2.2`	affected	semver	—
`0.2.3`	affected	semver	—
`0.2.4`	affected	semver	—
`0.2.5`	affected	semver	—
`0.2.6`	affected	semver	—
`0.2.7`	affected	semver	—
`0.2.8`	affected	semver	—
`0.2.9`	affected	semver	—
`0.2.10`	affected	semver	—
`0.2.11`	affected	semver	—
`0.2.12`	affected	semver	—
`0.2.13`	affected	semver	—
`0.2.14`	affected	semver	—
`0.2.15`	affected	semver	—
`0.2.16`	affected	semver	—
`0.2.17`	affected	semver	—
`0.2.18`	affected	semver	—
`0.2.19`	affected	semver	—
`0.2.20`	affected	semver	—
`0.2.21`	affected	semver	—
`0.2.22`	affected	semver	—
`0.2.23`	affected	semver	—
`0.2.24`	affected	semver	—
`0.2.25`	affected	semver	—
`0.2.26`	affected	semver	—
`0.2.27`	affected	semver	—
`0.2.28`	affected	semver	—
`0.2.29`	affected	semver	—
`0.2.30`	affected	semver	—
`0.2.31`	affected	semver	—
`0.2.32`	affected	semver	—
`0.2.33`	affected	semver	—
`0.2.34`	affected	semver	—
`0.2.35`	affected	semver	—
`0.2.36`	affected	semver	—

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

Source	ID	Title
Github GHSA	GHSA-f3q6-69f3-vwch	FastChat has a Content Moderation Bypass via Arena Side-by-Side Views

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact Low

Availability Impact None

User Interaction None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact Low

Availability Impact None

User Interaction None

Access Vector Network

Access Complexity Low

Authentication None

Confidentiality Impact None

Integrity Impact Partial

Availability Impact None

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.308% probability within 30 days)

Exploitation poc

Automatable yes

Technical Impact partial

References

Link	Providers
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

History

Apr 20, 2026 3:15 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Apr 20, 2026 6:15 AM Description updated. Title updated. First appearance in the feed. Weaknesses updated. Affected versions updated. Affected vendors updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
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.
Title		lm-sys fastchat Arena Side-by-Side View add_text control flow
First Time appeared		Lm-sys Lm-sys fastchat
Weaknesses		CWE-670
CPEs		cpe:2.3:a:lm-sys:fastchat::::::::
Vendors & Products		Lm-sys Lm-sys fastchat
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
Metrics		cvssV2_0 `{'score': 5, 'vector': 'AV:N/AC:L/Au:N/C:N/I:P/A:N/E:POC/RL:ND/RC:UR'}` cvssV3_0 `{'score': 5.3, 'vector': 'CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R'}` cvssV3_1 `{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N/E:P/RL:X/RC:R'}` cvssV4_0 `{'score': 6.9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P'}`