Chainlit up to 2.12.0 sessionId path traversal

Summaryinfo

A vulnerability classified as critical was found in Chainlit up to 2.12.0. The impacted element is an unknown function. Executing a manipulation of the argument sessionId can lead to path traversal. This vulnerability is handled as CVE-2026-86099. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability classified as critical was found in Chainlit up to 2.12.0. This vulnerability affects an unknown function. The manipulation of the argument sessionId with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-86099 since 09/05/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/09/2026). The MITRE ATT&CK project declares the attack technique as T1006.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Name

• Chainlit

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7
• 2.8
• 2.9
• 2.10
• 2.11
• 2.12.0

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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