fix(update): exclude npm candidates inside the launch directory subtree

src/update/npm-invocation.mjs

@@ -12,21 +12,17 @@ function escapeCmdCommand(command) {
   return command.replace(CMD_META, "^$1");
 }
 
-/**
- * Whether a PATH entry *is* the current directory. The hijack this guards against is
- * cmd.exe resolving a bare `npm` out of the directory opencodex was launched from, so
- * only that exact directory has to be skipped — every candidate we hand to spawn is an
- * absolute path, which is what actually defeats the implicit cwd-first search.
- *
- * Deliberately not a subtree test: npm's default Windows global prefix is
- * `%AppData%\npm` (`C:\Users\x\AppData\Roaming\npm`), so excluding everything under the
- * cwd would fail closed for anyone whose shell sits in their home directory — a normal
- * setup, not the untrusted-project case this hardening is for.
- */
-function isCurrentDirectory(cwd, entry) {
-  const left = win32.resolve(entry);
-  const right = win32.resolve(cwd);
-  return left.toLowerCase() === right.toLowerCase();
+function isInside(root, candidate) {
+  const relative = win32.relative(win32.resolve(root), win32.resolve(candidate));
+  return relative === "" || (
+    relative !== ".."
+    && !relative.startsWith(`..${win32.sep}`)
+    && !win32.isAbsolute(relative)
+  );
+}
+
+function isSamePath(left, right) {
+  return win32.resolve(left).toLowerCase() === win32.resolve(right).toLowerCase();
 }
 
 function cleanPathEntry(entry) {
@@ -43,6 +39,9 @@ export function resolveNpmCommand(
   if (platform !== "win32") return "npm";
   const exists = deps.exists ?? existsSync;
   const cwd = deps.cwd ?? process.cwd();
+  const appDataNpm = env.APPDATA && win32.isAbsolute(env.APPDATA)
+    ? win32.join(env.APPDATA, "npm")
+    : null;
   const extensions = (env.PATHEXT ?? ".COM;.EXE;.BAT;.CMD")
     .split(";")
     .filter(Boolean);
@@ -53,7 +52,8 @@ export function resolveNpmCommand(
 
   for (const entry of pathEntries) {
     if (!win32.isAbsolute(entry)) continue;
-    if (isCurrentDirectory(cwd, entry)) continue;
+    if (isSamePath(entry, cwd)) continue;
+    if (isInside(cwd, entry) && (!appDataNpm || !isSamePath(entry, appDataNpm))) continue;
     for (const extension of extensions) {
       const candidate = win32.join(entry, `npm${extension.toLowerCase()}`);
       if (exists(candidate)) return win32.resolve(candidate);

tests/update/update-npm-invocation.test.ts

@@ -45,6 +45,7 @@ describe("Windows npm update invocation", () => {
     const appDataNpm = `${home}\\AppData\\Roaming\\npm\\npm.cmd`;
     const env = {
       PATH: `${home}\\AppData\\Roaming\\npm`,
+      APPDATA: `${home}\\AppData\\Roaming`,
       PATHEXT: ".CMD",
       SystemRoot: "C:\\Windows",
     };
@@ -55,6 +56,28 @@ describe("Windows npm update invocation", () => {
     })).toBe(appDataNpm);
   });
 
+  test("ignores npm candidates in current-directory subtrees", () => {
+    const projectNpm = `${cwd}\\node_modules\\.bin\\npm.cmd`;
+    const env = {
+      PATH: `${cwd}\\node_modules\\.bin;C:\\Program Files\\nodejs`,
+      PATHEXT: ".CMD",
+      SystemRoot: "C:\\Windows",
+    };
+    const existing = new Set([projectNpm, trustedNpm]);
+
+    expect(resolveNpmCommand("win32", env, {
+      cwd,
+      exists: path => existing.has(path),
+    })).toBe(trustedNpm);
+
+    const invocation = npmInvocation(["install", "-g", "pkg@latest"], "win32", env, {
+      cwd,
+      exists: path => existing.has(path),
+    });
+    expect(invocation?.args.at(-1)).toContain("nodejs\\npm.cmd");
+    expect(invocation?.args.at(-1)).not.toContain("node_modules\\.bin\\npm.cmd");
+  });
+
   test("still skips the current directory when it is a PATH entry under the home tree", () => {
     // The narrower rule must not lose the actual defense: a PATH entry equal to the
     // launch directory stays excluded even though it sits inside the user's home.
@@ -92,4 +115,28 @@ describe("Windows npm update invocation", () => {
       exists: path => path === `${cwd}\\npm.cmd`,
     })).toBeNull();
   });
+
+  test("rejects the launch directory even when it is the trusted global npm prefix", () => {
+    // Regression: with cwd === %APPDATA%\npm the PATH entry equal to the launch
+    // directory satisfied both the subtree check and the trusted-prefix exception,
+    // re-admitting the exact current-directory candidate this hardening forbids.
+    const appData = "C:\\Users\\dev\\AppData\\Roaming";
+    const appDataNpmDir = `${appData}\\npm`;
+    const env = {
+      PATH: appDataNpmDir,
+      APPDATA: appData,
+      PATHEXT: ".CMD",
+      SystemRoot: "C:\\Windows",
+    };
+    const only = `${appDataNpmDir}\\npm.cmd`;
+
+    expect(resolveNpmCommand("win32", env, {
+      cwd: appDataNpmDir,
+      exists: path => path === only,
+    })).toBeNull();
+    expect(npmInvocation(["install", "-g", "pkg@latest"], "win32", env, {
+      cwd: appDataNpmDir,
+      exists: path => path === only,
+    })).toBeNull();
+  });
 });