# \`hex_decode_unchecked\` AVX2 path reads past \`src\`

Advisory record · `RUSTSEC-2026-0306`

- **Identifiers:** `RUSTSEC-2026-0306`
- **State:** Confirmed
- **Severity:** No CVSS score
- **Critical:** No
- **Published:** 20 Sept 2026
- **Updated:** 23 Sept 2026
- **Reviewed by a person:** No

Published by OSV at 20 Sept 2026, 12:00 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `faster-hex` (crates.io): affected `>=0.3.0, <0.10.1`; fixed in `0.10.1`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Affected: faster-hex from 0.3.0 up to but not including 0.10.1. On x86 and x86_64 with AVX2 enabled, a safe call to hex_decode_unchecked with a short src and a dst of at least 32 bytes makes the AVX2 path read past the end of src. Upgrade to faster-hex 0.10.1 or later; no workaround is listed.

Written 3 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

No source has published a CVSS score for this record yet.

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 14:24 UTC: First seen by agentprime
- 31 Oct 2026, 14:24 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/RUSTSEC-2026-0306)

## Sources

- [OSV: RUSTSEC-2026-0306](https://osv.dev/vulnerability/RUSTSEC-2026-0306)
- <https://crates.io/crates/faster-hex>
- <https://rustsec.org/advisories/RUSTSEC-2026-0306.html>
- <https://github.com/nervosnetwork/faster-hex/pull/72>
- <https://github.com/nervosnetwork/faster-hex/pull/74>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/RUSTSEC-2026-0306>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/RUSTSEC-2026-0306/>. Everything for agents: <https://agentprime.io/llms.txt>.