Vulnerabilities in pkg:pypi/fschat

PACKAGE
Advisory Identifier: GHSA-5h65-jx66-j7p5
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Advisory Summary

CVE-2026-6607 is a MODERATE (CVSS 5.3) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Fschat libraries in the PyPI ecosystem. The issue involves fastchat has denial of service through blocking event loop in model workers (incomplete fix for ff66426). Remediation is available in the latest vendor maintenance releases.

7 Known Advisory Record(s)
Package Vulnerability Intelligence

pkg:pypi/fschat

7 Known Advisory Record(s)

Vulnerability advisories affecting package pkg:pypi/fschat. Select an advisory below to view technical details or fixes.

Advisory ID CVE / NVD Severity Summary
GHSA-5h65-jx66-j7p5 CVE-2026-6607 MODERATE FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426)
GHSA-f3q6-69f3-vwch CVE-2026-6608 MODERATE FastChat has a Content Moderation Bypass via Arena Side-by-Side Views
GHSA-g44m-hpf4-vmrp CVE-2024-12376 HIGH FastChat Server-Side Request Forgery vulnerability
GHSA-h254-g997-685c CVE-2024-11603 HIGH FastChat Server-Side Request Forgery vulnerability
GHSA-qg86-f892-m4hj CVE-2024-10907 HIGH FastChat Uncontrolled Resource Consumption vulnerability
GHSA-77cj-rv5x-v6r2 CVE-2024-10908 MODERATE FastChat open redirect vulnerability
GHSA-79rp-v9rm-gxm8 CVE-2024-10912 HIGH FastChat Denial of Service vulnerability

CVE-2026-6607 at a Glance

CVE Identifier CVE-2026-6607
GHSA Identifier GHSA-5h65-jx66-j7p5
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Fschat
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-6607

To remediate this vulnerability, upgrade all affected Fschat dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

fschat fixed: Latest secure release 
pip install fschat>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show fschat

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-6607, inspect your installed packages using pip:

pip show fschat

Analyze the terminal output to locate any version of Fschat in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show fschat command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Fschat, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

A security vulnerability has been detected in lm-sys fastchat up to 0.2.36. This issue affects the function api_generate of the component Worker API Endpoint. The manipulation leads to resource consumption. The attack can be initiated remotely. The exploit has been disclosed publicly and may be used. The identifier of the patch is c9e84b89c91d45191dc24466888de526fa04cf33. It is suggested to install a patch to address this issue. Commit ff66426 patched this issue in api_generate of base_model_worker.py but missed other entry points.

CVE-2026-6607 Affected Fschat Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
fschat
pypi/fschat
PyPI
≤ 0.2.26

References

NVD — CVE-2026-6607 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6607
Fschat Source Repository REPOSITORY
https://github.com/lm-sys/FastChat/issues/3833
Fschat Source Repository REPOSITORY
https://github.com/lm-sys/FastChat/pull/3835
Security Fix Commit FIX COMMIT
https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33
Fschat Source Repository REPOSITORY
https://github.com/lm-sys/FastChat
Fschat Source Repository REPOSITORY
https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5
vuldb.com/submit/792227 WEB
https://vuldb.com/submit/792227
vuldb.com/vuln/358242 WEB
https://vuldb.com/vuln/358242
vuldb.com/vuln/358242/cti WEB
https://vuldb.com/vuln/358242/cti

Frequently Asked Questions

What is CVE-2026-6607?
CVE-2026-6607 is a security vulnerability in Fschat involving FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426) under CWE-400: Uncontrolled Resource Consumption.
Which Fschat versions are affected?
Affected versions include releases prior to current release patches across affected packages: fschat.
What version fixes CVE-2026-6607?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is fschat affected?
Yes, fschat is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-6607?
CVE-2026-6607 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-6607?
CVE-2026-6607 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check PyPI dependencies for CVE-2026-6607?
Run the dependency tree command: 'pip show fschat'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5h65-jx66-j7p5",
  "modified" : "2026-04-23T14:30:41Z",
  "published" : "2026-04-20T06:31:28Z",
  "aliases" : [ "CVE-2026-6607" ],
  "summary" : "FastChat has Denial of Service Through Blocking Event Loop in Model Workers (Incomplete Fix for ff66426)",
  "details" : "A security vulnerability has been detected in lm-sys fastchat up to 0.2.36. This issue affects the function api_generate of the component Worker API Endpoint. The manipulation leads to resource consumption. The attack can be initiated remotely. The exploit has been disclosed publicly and may be used. The identifier of the patch is c9e84b89c91d45191dc24466888de526fa04cf33. It is suggested to install a patch to address this issue. Commit ff66426 patched this issue in api_generate of base_model_worker.py but missed other entry points.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "fschat"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.2.26"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-6607"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lm-sys/FastChat/issues/3833"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lm-sys/FastChat/pull/3835"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lm-sys/FastChat/commit/c9e84b89c91d45191dc24466888de526fa04cf33"
  }, {
    "type" : "WEB",
    "url" : "https://gist.github.com/YLChen-007/87216a2d97a882d619e11dc67cd473b5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lm-sys/FastChat"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/submit/792227"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/358242"
  }, {
    "type" : "WEB",
    "url" : "https://vuldb.com/vuln/358242/cti"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-23T14:30:41Z",
    "nvd_published_at" : "2026-04-20T05:16:16Z"
  }
}