CVE-2026-86099 PUBLISHED

Chainlit through 2.12.0 Path Traversal via socket.io sessionId

Assigner: VulnCheck
Reserved: 04.09.2026 Published: 09.09.2026 Updated: 09.09.2026

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.

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
CVSS Score: 8.8

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	Low	Integrity	None
Attack Requirements	None	Availability	High	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
CVSS Score: 8.2

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Chainlit
Product	chainlit
Versions	Default: unaffected affected from 0 to 2.12.0 (incl.)

Credits

mil4n finder

References

Problem Types

CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') CWE