Zstd sys: WebAssembly allocator shim corrupts memory on allocation failure
Affects zstd-sysSource GCVE Database
Rated by Threat Radar
- Patch
- Available – fixed in 2.1.2
Data as of 26 Oct 2026, 16:13 UTC
What to do
Upgrade zstd-sys to 2.1.2.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
crates.iozstd-syspkg:cargo/zstd-sysOther threats | Affected
| Fixed in
|
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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.