GHSA-2jx3-ff3v-j7jj: 
Rust vulnerability analysis and mitigation

NOTE

This finding was identified during an agentic unsafe Rust code review performed by Gemini AI, followed by human review and verification.

The Issue

The crate exports a public safe API Rules::deserialize accepting any generic byte sequence B: AsRef<[u8]>. It restores compiled rule structures directly from raw bytes using bincode::serde::decode_from_slice. This decoded Rules struct contains internal lookup tables, including sub_patterns: Vec<(PatternId, SubPattern)>, atoms: Vec<SubPatternAtom>, and lit_pool: BStringPool. Subsequent safe operations assume these internal tables satisfy strict structural invariants:

• Rules::get_sub_pattern executes unsafe { self.sub_patterns.get_unchecked(sub_pattern_id.0 as usize) }. If untrusted serialized bytes contain an atom referencing an out-of-bounds SubPatternId, calling get_sub_pattern during scanning triggers an out-of-bounds memory read (Undefined Behavior). https://github.com/VirusTotal/yara-x/blob/5bd1f35db783679c90a3ea1a66bd15fe4e55bef1/lib/src/compiler/rules.rs#L355-L360
• Metadata::next() extracts string metadata via unsafe { s.to_str_unchecked() }. If serialized bytes corrupt lit_pool indices or structural data, to_str_unchecked constructs a &str pointing to invalid UTF-8 bytes (Undefined Behavior). https://github.com/VirusTotal/yara-x/blob/5bd1f35db783679c90a3ea1a66bd15fe4e55bef1/lib/src/models.rs#L204-L210 Because passing malformed or untrusted data to Rules::deserialize induces Undefined Behavior in subsequent safe calls (Scanner::new, Scanner::scan) without any unsafe blocks in caller code, this API is unsound.

<details><summary>Minimal Reproduction (Miri / Native Crash)</summary> Zip file with crashing_payload: crashing_payload.zip We have a payload crashing_payload.bin where only a single byte in the structural metadata tail is mutated (changing a SubPatternId from 1 to 248 while keeping the WebAssembly bytecode completely untouched and valid). Below is the self-contained verification script which compiles and runs against the official unmodified yara-x v1.17.0 crate:

use yara_x::{Rules, Scanner};
fn main() {
    // Embed the crashing payload generated by the fuzzer at compile time.
    let serialized = include_bytes!("crashing_payload.bin");
    println!("Loaded embedded crashing payload, length: {}", serialized.len());
    // Deserialize. On unmodified library, this succeeds because the WASM and headers
    // are pristine and structural corruption isn't validated.
    if let Ok(deserialized) = Rules::deserialize(serialized) {
        println!("Deserialization succeeded! Running scanner...");
        let mut scanner = Scanner::new(&deserialized);
        
        // Run the standard scan, which will execute the WASM and trigger the out-of-bounds read!
        let _ = scanner.scan(b"lorem ipsum dolor sit amet");
        println!("Scanner finished.");
    } else {
        println!("Deserialization failed!");
    }
}

1. Miri Trace

NOTE: This needs to be run with 1.17.0. I haven't tested this against other versions. Unfortunately I was able to get a miri trace, but I'm not able to reproduce it right now because of lockfile changes. If you're trying this out be sure to use MIRIFLAGS="-Zmiri-disable-stacked-borrows"

2. Segfault / panics

When run natively (without Miri or any sanitizers) on a standard Linux platform, the process immediately segfaults:

$ cargo run --bin verify
Loaded embedded crashing payload, length: 11777
Deserialization succeeded! Running scanner...
Segmentation fault (core dumped)

And with a newer compiler (which appears to have debug assertions in get_unchecked)

Deserialization succeeded! Running scanner...
thread 'main' (997442) panicked at lib/src/compiler/rules.rs:404:36:
unsafe precondition(s) violated: slice::get_unchecked requires that the index is within the slice
This indicates a bug in the program. This Undefined Behavior check is optional, and cannot be relied on for safety.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

</details> <details><summary>Suggested Fix</summary> To uphold Rust soundness guarantees, either mark Rules::deserialize as pub unsafe fn deserialize with a formal /// # Safety contract documenting that callers are responsible for verifying the authenticity and structural integrity of the input bytes (e.g. via cryptographic signatures), or replace all internal get_unchecked and to_str_unchecked calls on deserialized data structures with safe bounds checks (.get()) and UTF-8 validation (std::str::from_utf8). </details>