jxl-oxide is a pure Rust implementation of a JPEG XL decoder. Prior to jxl-grid 0.6.2, decoding a crafted JPEG XL image on a 32-bit platform can overflow length calculations in AlignedGrid::with_alloc_tracker and related grid and subgrid arithmetic. A 65536 x 65536 frame can pass the frame-area limit while overflowing the usize element count, causing modular, VarDCT, or filter rendering paths to allocate a backing buffer smaller than the logical grid. A tiny bitstream-controlled cropped frame combined with a huge canvas or requested region can also reach the vulnerable composition path in crates/jxl-render/src/blend.rs through ordinary render_frame(). Later mutable subgrid and raw-pointer operations can then perform attacker-controlled out-of-bounds writes, causing memory corruption, denial of service, or arbitrary code execution. This issue is fixed in jxl-grid version 0.6.2.

Affected: crates.io: jxl-grid

### Summary

On 32-bit platforms, decoding a crafted image may lead to out-of-bounds writes due to integer overflow in length calculation.

### Details & PoC

The test listed below fail under miri with command `cargo +nightly miri test --release -p jxl-grid`

Or you can use Address Sanitizer, which ignores Rust-specific UB like aliasing but still flags out-of-bounds accesses:

`RUSTFLAGS=-Zsanitizer=address cargo +nightly test -Zbuild-std -p jxl-grid --release --target x86_64-unknown-linux-gnu`

The following tests should be appended to `crates/jxl-grid/src/test/subgrids.rs`:

```rust mod miri_ub { use super::*;

// `AlignedGrid::with_alloc_tracker` computes `width * height` unchecked. In release, overflow // can create a tiny backing buffer for huge logical dimensions. #[test] fn aligned_grid_dimension_product_overflows() { let width = usize::MAX / 2 + 1; let mut grid = AlignedGrid::<u8>::with_alloc_tracker(width, 2, None).unwrap(); let mut subgrid = grid.as_subgrid_mut(); *subgrid.get_mut(0, 1) = 1; std::hint::black_box(grid); } } ```

This issue can be reachable through decoding a crafted image in two ways:

1. **Huge actual frame** A frame such as `65536 x 65536` passes the current frame area limit (`2^32 <= 2^40`) but overflows `usize` element count on 32-bit. Rendering then allocates too-small `AlignedGrid`s in modular/VarDCT/filter paths and later writes through mutable subgrids.

2. **Huge canvas plus…

Affected: crates.io: jxl-grid

On 32-bit platforms, decoding a crafted image may lead to out-of-bounds writes due to integer overflow in length calculation. This could allow arbitrary code execution.

### Details & PoC

The test listed below fail under miri with command `cargo +nightly miri test --release -p jxl-grid`

Or you can use Address Sanitizer, which ignores Rust-specific UB like aliasing but still flags out-of-bounds accesses:

`RUSTFLAGS=-Zsanitizer=address cargo +nightly test -Zbuild-std -p jxl-grid --release --target x86_64-unknown-linux-gnu`

The following tests should be appended to `crates/jxl-grid/src/test/subgrids.rs`:

```rust mod miri_ub { use super::*;

// `AlignedGrid::with_alloc_tracker` computes `width * height` unchecked. In release, overflow // can create a tiny backing buffer for huge logical dimensions. #[test] fn aligned_grid_dimension_product_overflows() { let width = usize::MAX / 2 + 1; let mut grid = AlignedGrid::<u8>::with_alloc_tracker(width, 2, None).unwrap(); let mut subgrid = grid.as_subgrid_mut(); *subgrid.get_mut(0, 1) = 1; std::hint::black_box(grid); } } ```

This issue can be reachable through decoding a crafted image in two ways:

1. **Huge actual frame** A frame such as `65536 x 65536` passes the current frame area limit (`2^32 <= 2^40`) but overflows `usize` element count on 32-bit. Rendering then allocates too-small `AlignedGrid`s in modular/VarDCT/filter paths and later writes through mutable su…