Path Traversal in Chainlit
CVE-2026-86099
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.
Vulnerability class: Path Traversal (Directory Traversal)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H.
EPSS exploit prediction
EPSS: 0.006 (48.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/Chainlit/chainlit (product)
- github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/session.py (technical-description)
- github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/socket.py (technical-description)
- pypi.org/project/chainlit/ (product)
- www.vulncheck.com/advisories/chainlit-through-2.12.0-path-traversal-via-socket-… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-86099?
- CVE-2026-86099 is a high-severity vulnerability in Chainlit, classified under Path Traversal. CVSS score: 8.2/10. Published 2026-09-09.
- How severe is CVE-2026-86099?
- High severity. CVSS v3 base score is 8.2 out of 10.