no_bidi_controls

Flag Trojan-Source bidi override characters (U+202A to U+202E, U+2066 to U+2069). Defense against CVE-2021-42574.

A text file with stray invalid UTF-8 is still scanned, so a junk byte cannot hide a control. A binary-looking file (for example one with a NUL byte) is scanned when it is valid UTF-8, so a NUL byte cannot hide a control in a crafted source file either; a binary-looking file that is not valid UTF-8 (images, fonts, archives) is skipped, which keeps paths: "**/*" free of false positives from random binary bytes. A finding in a binary-looking file is reported but not auto-fixed (file_strip_bidi refuses to edit binary content).

Options

This rule takes no kind-specific options.

Plus the common paths, level, id, when, scope_filter, fix, and expect_matches fields. This table is generated from the JSON Schema; option types and defaults are authoritative.

Example

A source file with a Trojan Source bidi override

The rule fires on this repository:

• src/
• src/clean.rs✓
• src/sneaky.rs✗

  ✗ error no-bidi

  1:16 Unicode bidi control U+202E at line 1 col 16 (Trojan-Source defense)

src/clean.rs

pub fn ok() {}

src/sneaky.rs

let comment = "<U+202E>gnitcepsnI ydobon emah sih";

With this .alint.yml:

version: 1
rules:
  - id: no-bidi
    kind: no_bidi_controls
    paths: "src/**/*.rs"
    level: error

alint check reports:

--- src/sneaky.rs --------------------------------------------------------------
  x  error    no-bidi
              1:16  Unicode bidi control U+202E at line 1 col 16 (Trojan-Source
              defense)

Summary (1 violation):
  x 1 error
  0 passing * 1 failing

Source files with ordinary emoji and no bidi controls

This repository is compliant:

• src/
• src/ascii.rs✓
• src/unicode.rs✓

src/ascii.rs

pub fn ok() {}

src/unicode.rs

// A ☃ comment with emoji 🦀
pub fn fine() {}

With this .alint.yml:

version: 1
rules:
  - id: no-bidi
    kind: no_bidi_controls
    paths: "src/**/*.rs"
    level: error

alint check reports:

v All 1 rule(s) passed.