---
id: CVE-2026-86099
title: >-
  Chainlit through 2.12.0 fails to validate the client-supplied socket.io
  sessionId parameter, allowing unauthenticated attackers to traverse filesystem
  paths by injecting absolute or relative path sequences
summary: >-
  Chainlit through 2.12.0 fails to validate the client-supplied socket.io
  sessionId parameter, allowing unauthenticated attackers to traverse filesystem
  paths by injecting absolute or relative path sequences. Attackers can craft
  malicious …
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H'
cwe:
  - CWE-22
vendor: Chainlit
product: chainlit
affected:
  - chainlit <= 2.12.0
published: '2026-09-09'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T20:20:21.673'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86099'
references:
  - url: 'https://github.com/Chainlit/chainlit'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/session.py
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/socket.py
    label: disclosure@vulncheck.com
  - url: 'https://pypi.org/project/chainlit/'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-io-sessionid
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-09T14:47:26.479403Z'
ingestedAt: '2026-09-09T14:11:29.381Z'
epss: 0.00598
epssPercentile: 0.46305
---

## Overview

Chainlit through 2.12.0 fails to validate the client-supplied socket.io sessionId parameter, allowing unauthenticated attackers to traverse filesystem paths by injecting absolute or relative path sequences. Attackers can craft malicious sessionId values that escape the upload directory and recursively delete arbitrary directories accessible to the service process.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.