# GHSA-2jx3-ff3v-j7jj: yara-x: Unvalidated deserialization in safe `Rules::deserialize` allows memory corruption and UB

> Unvalidated deserialization in yara-x allows attackers to trigger memory corruption and undefined behavior via crafted serialized rule data.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026

## What is GHSA-2jx3-ff3v-j7jj?

GHSA-2jx3-ff3v-j7jj is an unsafe deserialization vulnerability in yara-x, published on 24 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

> [!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`](https://github.com/VirusTotal/yara-x/blob/5bd1f35db783679c90a3ea1a66bd15fe4e55bef1/lib/src/compiler/rules.rs#L187-L254)  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](https://github.com/user-attachments/files/29173221/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:

```rust
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:

```bash
$ 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)`

```bash
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>

---

## Which versions are affected by GHSA-2jx3-ff3v-j7jj?

2 open source packages ship an affected version, including yara-x.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `yara-x` | crates.io | All versions | 1.19.0 |
| `yara-x` | crates.io | All versions | 1.19.0 |

## How do I fix GHSA-2jx3-ff3v-j7jj?

Upgrade yara-x to 1.19.0 or later.

## Is GHSA-2jx3-ff3v-j7jj being exploited?

There is no known exploitation of GHSA-2jx3-ff3v-j7jj in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-2jx3-ff3v-j7jj and fix it if it is affected.

What it is: GHSA-2jx3-ff3v-j7jj is an unsafe deserialization vulnerability in yara-x, published on 24 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-2jx3-ff3v-j7jj in the wild and no public exploit code.

Affected packages and fixed versions:
- yara-x (crates.io): affected all versions; fixed in 1.19.0
- yara-x (crates.io): affected all versions; fixed in 1.19.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/GHSA-2jx3-ff3v-j7jj/ (Markdown: https://insights.sbomify.com/GHSA-2jx3-ff3v-j7jj/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-2jx3-ff3v-j7jj

---
From sbomify Insights: https://insights.sbomify.com/GHSA-2jx3-ff3v-j7jj/
Summaries are generated and may contain mistakes; the official description above is the record.