---
id: "CVE-2026-120492"
kind: "vulnerability"
aliases: ["CVE-2026-120492"]
title: "Chainlit 2.12.0: semicolon in MCP URLs bypasses path-restricted allowed_urls"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "ai-tooling"
products: [{"name": "chainlit", "fixed": [], "affected": "2.12.0", "ecosystem": "pypi"}]
ecosystems: []
tags: ["ai-tooling", "chainlit", "mcp", "python", "self-hosted", "ssrf"]
not_affected_if: ["auth-required", "default-config", "mcp-disabled", "no-mcp"]
published_at: "2026-11-02T15:17:31+00:00"
first_seen_at: "2026-11-02T15:24:04+00:00"
updated_at: "2026-11-02T15:27:08+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120492", "first_seen_at": "2026-11-02T15:24:04+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-11-02T15:27:08+00:00"}]
---

# Chainlit 2.12.0: semicolon in MCP URLs bypasses path-restricted allowed_urls

Chainlit 2.12.0 fails to reject semicolons in MCP URLs, so the allowed_urls path restriction can be bypassed with '..;' segments sent to the /mcp endpoint. An unauthenticated attacker can make the server send requests to paths the operator did not grant, on origins that strip semicolon path parameters.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- pypi:chainlit affected 2.12.0 fixed ?

## How to check

Run 'pip show chainlit'; 2.12.0 is the version VulnCheck lists. Then check .chainlit/config.toml: you are exposed only if features.mcp.enabled = true, features.mcp.user_servers.enabled = true, and allowed_urls has a path-restricted entry (e.g. https://host/api) on a server that strips ';' path parameters (Java servlet containers and some proxies do). Also check whether you have no auth callback, since /mcp is then reachable anonymously. Also check 2.11.x and earlier: they have the broader SSRF CVE-2026-45019, fixed in 2.12.0.

## Fix

unknown: no patched version published for this bypass in the sources read. Check Chainlit releases after 2.12.0.

## Timeline

- 2026-11-02T15:24:04+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-120492
- 2026-11-02T15:27:08+00:00 analyst — Only VulnCheck states this bypass (affects 2.12.0). Linked GHSA-hvfh-5mj3-5f3j is the parent advisory for CVE-2026-45019 (fixed in 2.12.0), not this CVE; no Chainlit page for the semicolon bypass found, no fixed version published as far as I saw. Nothing verified.

## Documents

- [advisory] Vendor advisory: github.com https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/chainlit-2.12.0-ssrf-via-semicolon-path-segment-in-mcp-allowed-urls

## From the sources

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.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_