fix: reject path traversal and home-dir patterns in media parse layer (#54642)

* fix: reject path traversal and home-dir patterns in media parse layer

* Update parse tests

src/media/parse.test.ts

@@ -12,8 +12,6 @@ describe("splitMediaFromOutput", () => {
     const pathCases = [
       ["/Users/pete/My File.png", "MEDIA:/Users/pete/My File.png"],
       ["/Users/pete/My File.png", 'MEDIA:"/Users/pete/My File.png"'],
-      ["~/Pictures/My File.png", "MEDIA:~/Pictures/My File.png"],
-      ["../../etc/passwd", "MEDIA:../../etc/passwd"],
       ["./screenshots/image.png", "MEDIA:./screenshots/image.png"],
       ["media/inbound/image.png", "MEDIA:media/inbound/image.png"],
       ["./screenshot.png", "  MEDIA:./screenshot.png"],
@@ -31,6 +29,21 @@ describe("splitMediaFromOutput", () => {
     }
   });
 
+  it("rejects traversal and home-dir paths and strips them from output", () => {
+    const traversalCases = [
+      "MEDIA:../../../etc/passwd",
+      "MEDIA:../../.env",
+      "MEDIA:~/.ssh/id_rsa",
+      "MEDIA:~/Pictures/My File.png",
+      "MEDIA:./foo/../../../etc/shadow",
+    ];
+    for (const input of traversalCases) {
+      const result = splitMediaFromOutput(input);
+      expect(result.mediaUrls, `should reject media: ${input}`).toBeUndefined();
+      expect(result.text, `should strip from text: ${input}`).toBe("");
+    }
+  });
+
   it("keeps audio_as_voice detection stable across calls", () => {
     const input = "Hello [[audio_as_voice]]";
     const first = splitMediaFromOutput(input);

src/media/parse.ts

@@ -18,10 +18,21 @@ const WINDOWS_DRIVE_RE = /^[a-zA-Z]:[\\/]/;
 const SCHEME_RE = /^[a-zA-Z][a-zA-Z0-9+.-]*:/;
 const HAS_FILE_EXT = /\.\w{1,10}$/;
 
-// Recognize local file path patterns. Security validation is deferred to the
-// load layer (loadWebMedia / resolveSandboxedMediaSource) which has the context
-// needed to enforce sandbox roots and allowed directories.
-function isLikelyLocalPath(candidate: string): boolean {
+// Matches ".." as a standalone path segment (start, middle, or end).
+const TRAVERSAL_SEGMENT_RE = /(?:^|[/\\])\.\.(?:[/\\]|$)/;
+
+function hasTraversalOrHomeDirPrefix(candidate: string): boolean {
+  return (
+    candidate.startsWith("../") ||
+    candidate === ".." ||
+    candidate.startsWith("~") ||
+    TRAVERSAL_SEGMENT_RE.test(candidate)
+  );
+}
+
+// Broad structural check: does this look like a local file path? Used only for
+// stripping MEDIA: lines from output text — never for media approval.
+function looksLikeLocalFilePath(candidate: string): boolean {
   return (
     candidate.startsWith("/") ||
     candidate.startsWith("./") ||
@@ -33,6 +44,21 @@ function isLikelyLocalPath(candidate: string): boolean {
   );
 }
 
+// Recognize safe local file path patterns for media approval, rejecting
+// traversal and home-dir paths so they never reach downstream load/send logic.
+function isLikelyLocalPath(candidate: string): boolean {
+  if (hasTraversalOrHomeDirPrefix(candidate)) {
+    return false;
+  }
+  return (
+    candidate.startsWith("/") ||
+    candidate.startsWith("./") ||
+    WINDOWS_DRIVE_RE.test(candidate) ||
+    candidate.startsWith("\\\\") ||
+    (!SCHEME_RE.test(candidate) && (candidate.includes("/") || candidate.includes("\\")))
+  );
+}
+
 function isValidMedia(
   candidate: string,
   opts?: { allowSpaces?: boolean; allowBareFilename?: boolean },
@@ -54,6 +80,12 @@ function isValidMedia(
     return true;
   }
 
+  // Hard reject traversal/home-dir patterns before the bare-filename fallback
+  // to prevent path traversal bypasses (e.g. "../../.env" matching HAS_FILE_EXT).
+  if (hasTraversalOrHomeDirPrefix(candidate)) {
+    return false;
+  }
+
   // Accept bare filenames (e.g. "image.png") only when the caller opts in.
   // This avoids treating space-split path fragments as separate media items.
   if (opts?.allowBareFilename && !SCHEME_RE.test(candidate) && HAS_FILE_EXT.test(candidate)) {
@@ -169,7 +201,7 @@ export function splitMediaFromOutput(raw: string): {
 
       const trimmedPayload = payloadValue.trim();
       const looksLikeLocalPath =
-        isLikelyLocalPath(trimmedPayload) || trimmedPayload.startsWith("file://");
+        looksLikeLocalFilePath(trimmedPayload) || trimmedPayload.startsWith("file://");
       if (
         !unwrapped &&
         validCount === 1 &&