CVE-2026-120492

MEDIUM 5.4

Chainlit 2.12.0 SSRF via Semicolon Path Segment in MCP allowed_urls

CVSS Score

5.4

EPSS Score

0.0%

EPSS Percentile

0th

Chainlit 2.12.0 contains a server-side request forgery vulnerability that allows unauthenticated attackers to bypass path-scoped MCP allowed_urls entries because validate_mcp_url does not reject the semicolon character. Attackers can submit MCP URLs with '..;' segments to the /mcp endpoint, causing requests to paths outside the operator's grant on origins that strip semicolon path parameters.

CWE	CWE-918
Vendor	chainlit
Product	chainlit
Published	Nov 2, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

Chainlit / Chainlit

2.12.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j github.com: https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/mcp.py#L90-L177 github.com: https://github.com/Chainlit/chainlit/blob/2.12.0/backend/chainlit/mcp.py#L199-L208 vulncheck.com: https://www.vulncheck.com/advisories/chainlit-2.12.0-ssrf-via-semicolon-path-segment-in-mcp-allowed-urls

Credits

Gavin Blacklock