CVE-2026-120492
Deferred Deferred - Pending Action

Server-Side Request Forgery in Chainlit 2.12.0

Publication date: 2026-11-02

Last updated on: 2026-11-02

Assigner: VulnCheck

Description
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.

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Meta Information

Published
2026-11-02
Last Modified
2026-11-02
Generated
2026-11-02
AI Q&A
2026-11-02
EPSS Evaluated
N/A
NVD
CVE-2026-120492

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
Chainlit Chainlit 2.12.0

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-918 The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

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Executive Summary

CVE-2026-120492 is a Server-Side Request Forgery (SSRF) vulnerability in Chainlit 2.12.0. It allows unauthenticated attackers to bypass path-scoped MCP allowed_urls entries because the validate_mcp_url function does not reject semicolon characters in URLs. 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.

Detection Guidance

To detect this vulnerability, inspect Chainlit server logs for requests to the /mcp endpoint containing semicolon characters or '..;' segments in URLs. Check if MCP allowed_urls restrictions are bypassed by validating outbound requests against intended destinations. Use network monitoring tools to identify unauthorized outbound connections to internal or external services.

Impact Analysis

This vulnerability enables attackers to make unauthorized outbound HTTP requests to internal or external systems, including internal network services and cloud metadata endpoints. It could lead to port scanning, probing cloud services, or accessing sensitive internal APIs without authentication.

Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by enabling unauthorized data exfiltration or access to internal systems. The SSRF flaw allows attackers to make outbound requests to internal or external URLs, which may include sensitive endpoints like cloud metadata services or internal APIs. This could lead to unauthorized data access or disclosure, violating confidentiality requirements under both GDPR (Article 32) and HIPAA (Security Rule).

Mitigation Strategies

Upgrade Chainlit to a patched version beyond 2.12.0. Disable MCP features if unused. Configure strict allowlists for MCP URLs and strip restricted headers. Restrict outbound network egress to prevent unauthorized requests. Monitor for suspicious activity targeting the /mcp endpoint.

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