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WebAssembly allocator shim corrupts memory on allocation failure

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (zstd-sys 2.1.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • crates.io zstd-sys

    Affected
    >= 2.0.9, < 2.1.2
    Fixed in
    2.1.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
not scored
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

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.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from osv record RUSTSEC-2026-0410

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: rustsec-2026-0410

Advisory: WebAssembly allocator shim corrupts memory on allocation failure
IDs: rustsec-2026-0410
Record: https://patchnext.com/advisories/rustsec-2026-0410 (revision 1, source checked 27 Oct 2026, 06:25 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: zstd-sys 2.1.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io zstd-sys: affected >= 2.0.9, < 2.1.2; fixed in 2.1.2

## Suggested inspection (read-only)
- crates.io zstd-sys: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on zstd-sys.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0410 (OSV record RUSTSEC-2026-0410 lists affected ranges: crates.io zstd-sys >=2.0.9 <2.1.2 (fixed))

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