fix(security): sanitize control characters in prompt file error messages (#3141)

Reject file paths containing ASCII control characters (ANSI escape
sequences, null bytes, etc.) in validatePromptFilePath() to prevent
terminal injection. Also strip control chars in handlePromptFileError()
as defense-in-depth for error paths before validation.

Fixes #3138

Agent: security-auditor

Co-authored-by: B <6723574+louisgv@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: 3 people

packages/cli/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@openrouter/spawn",
-  "version": "0.30.5",
+  "version": "0.30.6",
   "type": "module",
   "bin": {
     "spawn": "cli.js"

packages/cli/src/__tests__/prompt-file-security.test.ts

@@ -1,7 +1,7 @@
 import { afterEach, beforeEach, describe, expect, it } from "bun:test";
 import { mkdirSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
 import { join } from "node:path";
-import { validatePromptFilePath, validatePromptFileStats } from "../security.js";
+import { stripControlChars, validatePromptFilePath, validatePromptFileStats } from "../security.js";
 
 describe("validatePromptFilePath", () => {
   it("should accept normal text file paths", () => {
@@ -158,6 +158,45 @@ describe("validatePromptFilePath", () => {
       expect(() => validatePromptFilePath(symlink)).not.toThrow();
     });
   });
+
+  it("should reject paths containing ANSI escape sequences", () => {
+    expect(() => validatePromptFilePath("\x1b[2J\x1b[Hfake.txt")).toThrow("control characters");
+    expect(() => validatePromptFilePath("file\x1b[31mred.txt")).toThrow("control characters");
+  });
+
+  it("should reject paths containing null bytes", () => {
+    expect(() => validatePromptFilePath("file\x00.txt")).toThrow("control characters");
+  });
+
+  it("should reject paths containing other control characters", () => {
+    expect(() => validatePromptFilePath("file\x07bell.txt")).toThrow("control characters");
+    expect(() => validatePromptFilePath("file\x08backspace.txt")).toThrow("control characters");
+    expect(() => validatePromptFilePath("file\x7Fdel.txt")).toThrow("control characters");
+  });
+});
+
+describe("stripControlChars", () => {
+  it("should strip ANSI escape sequences", () => {
+    expect(stripControlChars("\x1b[2J\x1b[Hfake.txt")).toBe("[2J[Hfake.txt");
+  });
+
+  it("should strip null bytes", () => {
+    expect(stripControlChars("file\x00.txt")).toBe("file.txt");
+  });
+
+  it("should strip bell, backspace, and DEL", () => {
+    expect(stripControlChars("file\x07\x08\x7F.txt")).toBe("file.txt");
+  });
+
+  it("should preserve tabs and newlines", () => {
+    expect(stripControlChars("line1\nline2\ttab")).toBe("line1\nline2\ttab");
+  });
+
+  it("should return normal strings unchanged", () => {
+    expect(stripControlChars("/tmp/prompt.txt")).toBe("/tmp/prompt.txt");
+    expect(stripControlChars("")).toBe("");
+    expect(stripControlChars("hello world")).toBe("hello world");
+  });
 });
 
 describe("validatePromptFileStats", () => {

packages/cli/src/index.ts

@@ -317,19 +317,24 @@ async function suggestCloudsForPrompt(agent: string): Promise<void> {
 
 /** Print a descriptive error for a failed prompt file read and exit */
 function handlePromptFileError(promptFile: string, err: unknown): never {
+  // SECURITY: Strip control characters to prevent terminal injection via crafted paths.
+  // validatePromptFilePath() rejects these early, but this is defense-in-depth for
+  // error paths that run before validation (e.g., stat failures).
+  // Inline the same regex from security.ts to avoid async import in a sync function.
+  const safePath = promptFile.replace(/[\x00-\x08\x0B-\x1F\x7F]/g, "");
   const errObj = toRecord(err);
   const code = isString(errObj?.code) ? errObj.code : "";
   if (code === "ENOENT") {
-    console.error(pc.red(`Prompt file not found: ${pc.bold(promptFile)}`));
+    console.error(pc.red(`Prompt file not found: ${pc.bold(safePath)}`));
     console.error("\nCheck the path and try again.");
   } else if (code === "EACCES") {
-    console.error(pc.red(`Permission denied reading prompt file: ${pc.bold(promptFile)}`));
-    console.error(`\nCheck file permissions: ${pc.cyan(`ls -la ${promptFile}`)}`);
+    console.error(pc.red(`Permission denied reading prompt file: ${pc.bold(safePath)}`));
+    console.error(`\nCheck file permissions: ${pc.cyan(`ls -la ${safePath}`)}`);
   } else if (code === "EISDIR") {
-    console.error(pc.red(`'${promptFile}' is a directory, not a file.`));
+    console.error(pc.red(`'${safePath}' is a directory, not a file.`));
     console.error("\nProvide a path to a text file containing your prompt.");
   } else {
-    console.error(pc.red(`Error reading prompt file '${promptFile}': ${getErrorMessage(err)}`));
+    console.error(pc.red(`Error reading prompt file '${safePath}': ${getErrorMessage(err)}`));
   }
   process.exit(1);
 }

packages/cli/src/security.ts

@@ -553,6 +553,18 @@ export function validateTunnelPort(port: string): void {
   }
 }
 
+/**
+ * Strip ASCII control characters from a string for safe terminal display.
+ * Removes characters 0x00-0x1F and 0x7F, preserving tab (0x09) and newline (0x0A).
+ * SECURITY-CRITICAL: Prevents ANSI escape sequence injection in error messages.
+ *
+ * @param s - The string to sanitize
+ * @returns The string with control characters removed
+ */
+export function stripControlChars(s: string): string {
+  return s.replace(/[\x00-\x08\x0B-\x1F\x7F]/g, "");
+}
+
 // Sensitive path patterns that should never be read as prompt files
 // These protect credentials and system files from accidental exfiltration
 const SENSITIVE_PATH_PATTERNS: ReadonlyArray<{
@@ -632,6 +644,16 @@ export function validatePromptFilePath(filePath: string): void {
     );
   }
 
+  // Reject paths containing control characters (ANSI escape sequences, null bytes, etc.)
+  // These can cause terminal injection when displayed in error messages.
+  if (/[\x00-\x08\x0B-\x1F\x7F]/.test(filePath)) {
+    throw new Error(
+      "Prompt file path contains control characters (e.g., ANSI escape sequences).\n\n" +
+        "File paths must be plain text without terminal control codes.\n" +
+        "Check that the path was entered correctly.",
+    );
+  }
+
   // Normalize the path to resolve .. and textual tricks
   let resolved = resolve(filePath);