Unauthenticated moderation bypass via omitted conversation history
Published Apr 20, 2026 · Updated Apr 20, 2026
Content moderation bypass in LMSYS FastChat 0.2.36 and earlier allows remote attackers to evade Arena conversation-history checks. Two add_text handlers read the left conversation state twice, while a third passes only current text to moderate_input instead of full history. Exploitation requires multi-turn side-by-side chat with moderation enabled and leaves prior model output outside content-policy enforcement.
Summary
What happened
Content moderation bypass in LMSYS FastChat 0.2.36 and earlier allows remote attackers to evade Arena conversation-history checks. Two add_text handlers read the left conversation state twice, while a third passes only current text to moderate_input instead of full history. Exploitation requires multi-turn side-by-side chat with moderation enabled and leaves prior model output outside content-policy enforcement.
The record
- CVE
- CVE-2026-6608
- Published
- Apr 20, 2026
- Updated
- Apr 20, 2026
- Vendor
- LMSYS Org
- Product
- FastChat
- Classifications
- CWE-670, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 20, 2026CVE publishedPublication date reported by the CVE source.
- Apr 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0.2.0
- Affected versionversion=0.2.1
- Affected versionversion=0.2.10
- Affected versionversion=0.2.11
- Affected versionversion=0.2.12
- Affected versionversion=0.2.13
- Affected versionversion=0.2.14
- Affected versionversion=0.2.15
- Affected versionversion=0.2.16
- Affected versionversion=0.2.17
- Affected versionversion=0.2.18
- Affected versionversion=0.2.19
- Affected versionversion=0.2.2
- Affected versionversion=0.2.20
- Affected versionversion=0.2.21
- Affected versionversion=0.2.22
- Affected versionversion=0.2.23
- Affected versionversion=0.2.24
- Affected versionversion=0.2.25
- Affected versionversion=0.2.26
- Affected versionversion=0.2.27
- Affected versionversion=0.2.28
- Affected versionversion=0.2.29
- Affected versionversion=0.2.3
- Affected versionversion=0.2.30
- Affected versionversion=0.2.31
- Affected versionversion=0.2.32
- Affected versionversion=0.2.33
- Affected versionversion=0.2.34
- Affected versionversion=0.2.35
- Affected versionversion=0.2.36
- Affected versionversion=0.2.4
- Affected versionversion=0.2.5
- Affected versionversion=0.2.6
- Affected versionversion=0.2.7
- Affected versionversion=0.2.8
- Affected versionversion=0.2.9
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Content Moderation Bypass in Arena Side-by-Side Views proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo