From 9b853ce960f1bcbc33fde3a6b7f677152a6bf889 Mon Sep 17 00:00:00 2001
From: jeremymcs <jeremymcs@users.noreply.github.com>
Date: Fri, 10 Apr 2026 15:06:01 -0400
Subject: [PATCH] fix(mcp-server): URL scheme regex no longer matches Windows
 drive letters

Change /^[a-z]+:/i to /^[a-z]{2,}:/i in getWriteGateModuleCandidates()
and getWorkflowExecutorModuleCandidates() so single-letter drive prefixes
(C:, D:) are not rejected as URL schemes. All IANA-registered schemes are
2+ characters, so this is a safe narrowing.

Adds regression tests for the regex fix.

Fixes #3942
---
 .../mcp-server/src/workflow-tools.test.ts     | 28 +++++++++++++++++++
 packages/mcp-server/src/workflow-tools.ts     |  4 +--
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/packages/mcp-server/src/workflow-tools.test.ts b/packages/mcp-server/src/workflow-tools.test.ts
index 35a883b3b..74ee74a85 100644
--- a/packages/mcp-server/src/workflow-tools.test.ts
+++ b/packages/mcp-server/src/workflow-tools.test.ts
@@ -974,3 +974,31 @@ describe("workflow MCP tools", () => {
     }
   });
 });
+
+describe("URL scheme regex — Windows drive letter safety", () => {
+  // This is the regex used in getWriteGateModuleCandidates() and
+  // getWorkflowExecutorModuleCandidates() to reject non-file URL schemes.
+  // It must NOT match single-letter Windows drive prefixes (C:, D:, etc.).
+  const urlSchemeRegex = /^[a-z]{2,}:/i;
+
+  it("rejects multi-letter URL schemes", () => {
+    assert.ok(urlSchemeRegex.test("http://example.com"), "http: should match");
+    assert.ok(urlSchemeRegex.test("https://example.com"), "https: should match");
+    assert.ok(urlSchemeRegex.test("ftp://files.example.com"), "ftp: should match");
+    assert.ok(urlSchemeRegex.test("file:///C:/Users"), "file: should match");
+    assert.ok(urlSchemeRegex.test("node:fs"), "node: should match");
+  });
+
+  it("allows single-letter Windows drive prefixes", () => {
+    assert.ok(!urlSchemeRegex.test("C:\\Users\\user\\project"), "C:\\ should not match");
+    assert.ok(!urlSchemeRegex.test("D:\\other\\path"), "D:\\ should not match");
+    assert.ok(!urlSchemeRegex.test("c:\\lowercase\\drive"), "c:\\ should not match");
+    assert.ok(!urlSchemeRegex.test("E:/forward/slash/path"), "E:/ should not match");
+  });
+
+  it("allows bare filesystem paths", () => {
+    assert.ok(!urlSchemeRegex.test("/usr/local/lib/module.js"), "unix absolute path should not match");
+    assert.ok(!urlSchemeRegex.test("./relative/path.js"), "relative path should not match");
+    assert.ok(!urlSchemeRegex.test("../parent/path.js"), "parent relative path should not match");
+  });
+});
diff --git a/packages/mcp-server/src/workflow-tools.ts b/packages/mcp-server/src/workflow-tools.ts
index 95ea20494..1f3b3af97 100644
--- a/packages/mcp-server/src/workflow-tools.ts
+++ b/packages/mcp-server/src/workflow-tools.ts
@@ -318,7 +318,7 @@ function getWriteGateModuleCandidates(): string[] {
   const candidates: string[] = [];
   const explicitModule = process.env.GSD_WORKFLOW_WRITE_GATE_MODULE?.trim();
   if (explicitModule) {
-    if (/^[a-z]+:/i.test(explicitModule) && !explicitModule.startsWith("file:")) {
+    if (/^[a-z]{2,}:/i.test(explicitModule) && !explicitModule.startsWith("file:")) {
       throw new Error("GSD_WORKFLOW_WRITE_GATE_MODULE only supports file: URLs or filesystem paths.");
     }
     candidates.push(explicitModule.startsWith("file:") ? explicitModule : toFileUrl(explicitModule));
@@ -340,7 +340,7 @@ function getWorkflowExecutorModuleCandidates(env: NodeJS.ProcessEnv = process.en
   const candidates: string[] = [];
   const explicitModule = env.GSD_WORKFLOW_EXECUTORS_MODULE?.trim();
   if (explicitModule) {
-    if (/^[a-z]+:/i.test(explicitModule) && !explicitModule.startsWith("file:")) {
+    if (/^[a-z]{2,}:/i.test(explicitModule) && !explicitModule.startsWith("file:")) {
       throw new Error("GSD_WORKFLOW_EXECUTORS_MODULE only supports file: URLs or filesystem paths.");
     }
     candidates.push(explicitModule.startsWith("file:") ? explicitModule : toFileUrl(explicitModule));