pdftract/notes/bf-ieaa9.md

bf-ieaa9: Verify no JavaScript execution during extraction

Summary

Verified that pdftract does NOT execute embedded JavaScript during PDF extraction, confirming the TH-04 threat model mitigation.

What Was Done

1. Dependency Verification

• Verified no JavaScript engine dependencies in the cargo tree
• Confirmed absence of: boa, deno_core, v8, quickjs, rusty_javascript, rquickjs, js-sys
• Without a JS engine, JavaScript execution is impossible at the binary level

2. Code Review: src/javascript.rs

• Confirmed only string extraction via String::from_utf8_lossy()
• No eval(), exec(), or any code execution primitives
• Added comprehensive security boundary documentation (TH-04) explaining:
  • No JavaScript Engine: No dependency on JS execution engines
  • String-Only Processing: JavaScript code extracted as raw byte strings
  • Explicit Diagnostic: Emits "JavaScript was NOT executed" message

3. Enhanced Test Coverage: tests/TH-04-js-presence.rs

• Added explicit assertion that diagnostic states "JavaScript was NOT executed"
• Added security boundary verification comments explaining why no side effects occur
• Enhanced test_no_js_engine_in_deps() with comprehensive documentation
• All 4 tests pass: test_javascript_detection, test_no_javascript, test_no_js_engine_in_deps, test_json_output_includes_javascript_actions

4. Runtime Verification

Extracted tests/fixtures/security/embedded-js.pdf which contains:

• app.alert("pwn") in catalog /OpenAction
• app.alert('page_open') in page 0 /AA/O
• app.alert('annot_action') in page 1 annotation /A

Result:

• Extraction succeeded (exit 0)
• Diagnostic emitted: "Detected 1 JavaScript action(s) in PDF document. JavaScript was NOT executed."
• No app.alert() popup displayed (no side effects)
• JavaScript extracted as string data only: "app.alert(\"pwn\")"

Acceptance Criteria

• ✅ PASS: Extraction completes without executing JavaScript

  • Verified: Extracted embedded-js.pdf successfully, no side effects occurred
  • No panic, abort, or popup from app.alert() calls

• ✅ PASS: No app.alert or other JS side effects occur

  • The fixture contains app.alert("pwn") which would display a dialog if executed
  • No alert was shown - extraction completed normally
  • Confirmed by reaching test assertions without interruption

• ✅ PASS: Test or code explicitly verifies non-execution

  • Added explicit assertion: diagnostics.iter().any(|d| d.contains("JavaScript was NOT executed"))
  • Added comprehensive security boundary documentation in src/javascript.rs
  • Enhanced test_no_js_engine_in_deps() with threat model compliance explanation

• ✅ PASS: Security boundary is documented in code comments

  • Added detailed security boundary documentation in src/javascript.rs header
  • Documented string-only processing (no evaluation/parsing/execution)
  • Explained threat model compliance (TH-04 mitigation)
  • Added inline comments in tests explaining why no side effects occur

Verification Files

• /home/coding/pdftract/crates/pdftract-core/src/javascript.rs - Security boundary documentation
• /home/coding/pdftract/crates/pdftract-core/tests/TH-04-js-presence.rs - Enhanced test coverage
• /home/coding/pdftract/tests/fixtures/security/embedded-js.pdf - Test fixture with JavaScript

Threat Model Compliance

TH-04: "JavaScript embedded in /AA, /OpenAction, or /JS entries triggers execution"

Mitigation: "pdftract NEVER executes embedded JavaScript; presence is flagged as a JAVASCRIPT_PRESENT diagnostic (info-level) and surfaced in the JSON output as metadata.javascript_actions[] for downstream review"

Status: ✅ VERIFIED - JavaScript is detected but NOT executed