mozilla/pdf.js · error · Error

Cannot start sandbox

Error message

Cannot start sandbox

What it means

Thrown by the QuickJS sandbox bootstrap when the WASM module failed to initialize (the internal `success` flag is false). The sandbox is required to execute interactive PDF form JavaScript safely, so a failed start nukes the sandbox and aborts scripting support. It is an environment/loading failure, not a PDF-content failure.

Source

Thrown at src/pdf.sandbox.js:98

        [buf, this._alertOnError]
      );
    } catch (error) {
      // eslint-disable-next-line no-console
      console.error(error);
    } finally {
      if (buf) {
        this._module.ccall("free", "number", ["number"], [buf]);
      }
    }

    if (success) {
      this.support.commFun = this._module.cwrap("commFun", null, [
        "string",
        "string",
      ]);
    } else {
      this.nukeSandbox();
      throw new Error("Cannot start sandbox");
    }
  }

  dispatchEvent(event) {
    this.support?.callSandboxFunction("dispatchEvent", event);
  }

  dumpMemoryUse() {
    this._module?.ccall("dumpMemoryUse", null, []);
  }

  nukeSandbox() {
    if (this._module !== null) {
      this.support.destroy();
      this.support = null;
      this._module.ccall("nukeSandbox", null, []);
      this._module = null;
    }

View on GitHub (pinned to 5903d58d58)

Solutions

1. Ensure the sandbox WASM asset is served with the correct MIME type and is reachable.
2. Allow WASM in CSP (add 'wasm-unsafe-eval' to script-src, or loosen worker-src).
3. Use matching versions of the PDF.js API and the sandbox bundle.
4. Verify the runtime supports WebAssembly.

// Ensure the sandbox asset is reachable and CSP allows WASM before enabling scripting.
// headers: Content-Security-Policy: script-src 'self' 'wasm-unsafe-eval';

function runtimeSupportsWasm() {
  return typeof WebAssembly === 'object' && typeof WebAssembly.compile === 'function';
}

try {
  await pdfjsSandboxInit();
} catch (e) {
  if (e.message === 'Cannot start sandbox') {
    // disable interactive form scripting; forms still display
  }
}

When it happens

Trigger: The sandbox setup routine runs to completion but reports failure: the WASM module did not compile/instantiate or its entry points are missing; nukeSandbox() is called then the error is thrown.

Common situations: Content-Security-Policy blocks WASM ('wasm-unsafe-eval' or script-src too strict); the pdf.sandbox wasm asset is missing or 404; a build version mismatch between sandbox loader and wasm; an out-of-memory or unsupported-WASM environment.

Related errors

• Cannot create sandbox.
• The PDF file is empty, i.e. its size is zero bytes.
• No ICC color space support
• JBig2 failed to initialize
• OpenJPEG failed to initialize

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/f304c10759a6092c. Report an issue: GitHub.