---
title: "CVE-2026-86099: Chainlit - Path Traversal"
description: "Chainlit through 2.12.0 contains a path traversal caused by improper validation of client-supplied socket.io sessionId parameter, letting unauthenticated attackers delete arbitrary directories, exploit requires crafted sessionId values."
url: https://panop.io/threat-heartbeat/CVE-2026-86099/
---

# CVE-2026-86099 Chainlit - Path Traversal

Chainlit through 2.12.0 contains a path traversal caused by improper validation of client-supplied socket.io sessionId parameter, letting unauthenticated attackers delete arbitrary directories, exploit requires crafted sessionId values.

CVSS base score 8.2 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.60% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-86099)

## Details

Type

Path Traversal

Impact

Denial Of Service, File System Write

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Published

9 September 2026

Updated

15 October 2026

Weakness

[CWE-22](https://cwe.mitre.org/data/definitions/22.html)

## Vendor fix

Update to the latest version.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-86099](https://nvd.nist.gov/vuln/detail/CVE-2026-86099)
- [https://pypi.org/project/chainlit/](https://pypi.org/project/chainlit/)
- [https://www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-io-sessionid](https://www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-io-sessionid)
- [https://github.com/Chainlit/chainlit](https://github.com/Chainlit/chainlit)
- [https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/session.py](https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/session.py)
- [https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/socket.py](https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/socket.py)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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