High severity · published Sep 9, 2026
CVE-2026-86099
Chainlit through 2.12.0 Path Traversal via socket.io sessionId
8.2
CVSS
0.6%
EPSS
No
On KEV
Description
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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
Low
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 48% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CH
chainlit · Chainlit
through 2.12.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-86099
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-86099
github.com
https://github.com/Chainlit/chainlit
github.com
https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/session.py
github.com
https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/socket.py
pypi.org
https://pypi.org/project/chainlit/
www.vulncheck.com
https://www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-io-sessionid
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