Reported

October 16, 2026

Issued

October 26, 2026

Package

zstd-sys (crates.io)

Type

Vulnerability

Categories

• memory-corruption

Keywords

#wasm #allocation

References

• https://github.com/gyscos/zstd-rs/commit/165d1625553c236b9700ca794b8a7c51f5d98314
• https://github.com/gyscos/zstd-rs/pull/384

Patched

• >=2.1.2

Unaffected

• <2.0.9

Affected Architectures

• wasm32

Description

On wasm32, zstd-sys provides malloc and free to the C library through a shim over Rust's allocator. The shim did not check for allocation failure: it wrote its size header to address 0 and returned address 4, which the C library used as a valid buffer. free(NULL) also read below address 0.

Whenever the instance cannot grow its memory by what a frame asks for, a small crafted frame (a 9-byte header declaring a 128 MiB window is enough) made decompression write decoded data over the bottom of the module's linear memory, instead of failing. The corruption stays within the wasm sandbox.

The flaw was corrected by returning NULL on allocation failure or size overflow, and by making free(NULL) a no-op.

Advisory available under CC0-1.0 license.