# RUSTSEC-2026-0329: Auto-Reseeding HMAC-DRBG could panic for some output lengths

> Applications using libcrux-hmac-drbg may panic when requesting specific large output lengths, causing a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Aug 2026

## What is RUSTSEC-2026-0329?

RUSTSEC-2026-0329 is a denial of service vulnerability in libcrux-hmac-drbg, published on 3 Aug 2026. 

### Official description

The automatically reseeding implementations of HMAC-DRBG would panic if called with a desired non-zero output length cleanly divisible by `65_536`, the maximum number of output bytes that can be generated before reseeding has to happen.

# Impact

An application relying on `libcrux-hmac-drgb` to provide randomness of byte length a non-zero integer multiple of `65_536` in a single call to `fill_bytes` would panic.

Any calls with output buffer lengths not cleanly divisible by `65_536` are not affected.

# Mitigation

With release the release of version `0.0.2` of `libcrux-hmac-drbg` this bug has been fixed and reseeding DRBG implementations can be used with arbitrary output lengths.

We recommend users upgrade to `libcrux-hmac-drbg` version `0.0.2`.

## Which versions are affected by RUSTSEC-2026-0329?

1 open source package ship an affected version, including libcrux-hmac-drbg.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `libcrux-hmac-drbg` | crates.io | From 0.0.0-0 | 0.0.2 |

## How do I fix RUSTSEC-2026-0329?

Upgrade libcrux-hmac-drbg to 0.0.2 or later.

## Is RUSTSEC-2026-0329 being exploited?

There is no known exploitation of RUSTSEC-2026-0329 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0329 and fix it if it is affected.

What it is: RUSTSEC-2026-0329 is a denial of service vulnerability in libcrux-hmac-drbg, published on 3 Aug 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0329 in the wild and no public exploit code.

Affected packages and fixed versions:
- libcrux-hmac-drbg (crates.io): affected from 0.0.0-0; fixed in 0.0.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/RUSTSEC-2026-0329/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0329/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0329

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0329/
Summaries are generated and may contain mistakes; the official description above is the record.