# zstd-safe Seekable decompress buffer overrun on invalid offset

Source: https://junglewise.ai/threats/rustsec-2026-0398-seekable-decompress-sets-a-vec-length-beyond-its-2f278ece  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-16. Updated: 2026-10-28  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-10-16

The zstd-safe Rust library, which provides compression and decompression functionality, contains a flaw in its seekable decompression feature. When processing archives with offsets past the end of the data, the library incorrectly sets a buffer's length to a value exceeding its capacity, allowing attackers to read adjacent heap memory or cause memory corruption. Applications using the seekable feature with untrusted archives face heap information disclosure and potential denial of service.

Technologies: [zstd-safe (crates.io)](https://junglewise.ai/threats/technologies/zstd-safe), [Gyscos Zstd-Safe](https://junglewise.ai/threats/technologies/gyscos-zstd-safe). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io), [Gyscos](https://junglewise.ai/threats/vendors/gyscos).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 16 October 2026.

**Which products and versions are affected?** zstd-safe (crates.io) SEMVER:introduced=7.2.2,fixed=8.2.0; Gyscos Zstd-Safe 7.2.2 to 8.1.x.

**Is there a fix for This vulnerability?** Yes. zstd-safe (crates.io): upgrade to 8.2.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network.

**Am I affected?** Check whether you run zstd-safe (crates.io) or Gyscos Zstd-Safe at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- zstd-safe (crates.io): upgrade to 8.2.0 or later

  ```sh
  cargo update -p zstd-safe
  ```


## Technical details

The vulnerability exists in `Seekable::decompress` and `AdvancedSeekable::decompress` functions (versions 7.2.2 to 8.1.x). The underlying C function `ZSTD_seekable_decompress` returns a wrapped-around length when given an offset past the end of the data, which the Rust wrapper incorrectly passes to `Vec::set_len` without validating against buffer capacity. This causes heap memory disclosure on read and corruption on append; additionally, offsets near `u64::MAX` can cause the call to hang. The fix validates all counts against buffer capacity and clamps requests to the end of the data.

## Affected products

- gyscos zstd-safe 7.2.2 to 8.1.x

## Timeline

- 2026-10-16: disclosed
- 2026-10-26: patched

## References

- [https://crates.io/crates/zstd-safe](https://crates.io/crates/zstd-safe)
- [https://rustsec.org/advisories/RUSTSEC-2026-0398.html](https://rustsec.org/advisories/RUSTSEC-2026-0398.html)

## Related threats

- [zstd-safe use-after-free in multithreaded compression context](https://junglewise.ai/threats/rustsec-2026-0406-use-after-free-when-changing-a-multithreaded-context-0c474512)
- [zstd-safe double free in DCtx::try_clone](https://junglewise.ai/threats/rustsec-2026-0404-double-free-in-dctx-try-clone-108878f4)
- [zstd-safe Seekable null or out-of-bounds seek table read](https://junglewise.ai/threats/rustsec-2026-0396-seekable-reads-a-null-or-out-of-bounds-seek-table-4b9e21ae)
- [zstd-safe use-after-free in dictionary decompression context](https://junglewise.ai/threats/rustsec-2026-0400-use-after-free-of-a-dictionary-after-a-one-shot-call-541157eb)
- [zstd-safe out-of-bounds read in seekable stream compression](https://junglewise.ai/threats/rustsec-2026-0405-out-of-bounds-read-with-an-out-of-range-inbuffer-pos-610ef200)