Vulnerability record · CVE-2026-86099 · published 9 September 2026

CVE-2026-86099: Path traversal vulnerability

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.

8.8 CVSS 4.0 High EPSS 0.60% · top 53.5% CWE-22 · Path traversal Deferred

8.8CVSS 4.0 base score

0.60%EPSS exploitation probability, 30 days

NoNot in CISA KEV

0Affected product versions listed by NVD

5References

9 Sep 2026Last modified by NVD

Description

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

Link	Tags
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/socket.py
https://pypi.org/project/chainlit/
https://www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-io-sessionid

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-86099), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.