# RUSTSEC-2026-0340: Peer minimum ACK delay can panic quinn-proto when ACK_FREQUENCY transmission is enabled

> A remote attacker can cause a denial of service by sending crafted transport parameters to a quinn-proto server with ACK frequency enabled.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 14 Sep 2026
- **Also known as:** GHSA-3g6h-r5qx-f6hq

## What is RUSTSEC-2026-0340?

RUSTSEC-2026-0340 is a denial of service vulnerability in quinn-proto, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When sending ACK_FREQUENCY frames is enabled through
`TransportConfig::ack_frequency_config(Some(..))`, the peer's transport parameters could cause
`AckFrequencyState::candidate_max_ack_delay` to call `Duration::clamp` with a minimum greater
than its maximum, which panics.

For example, a peer advertising a `min_ack_delay` of 100,000 microseconds and a `max_ack_delay`
of 100 milliseconds passes transport parameter validation. At a 5 ms RTT, the lower bound of the
clamp becomes 100 ms while the upper bound is 25 ms, violating the precondition of `clamp` and
panicking while driving the connection. Both automatically derived and explicitly configured
maximum ACK delays use this calculation.

Sending ACK_FREQUENCY frames is disabled by default, so only endpoints that opt in are affected.

The flaw was corrected in 0.11.18 by computing the delay with explicit minimum and maximum bounds
instead of `clamp`.

Thanks to [@zerox80](https://github.com/zerox80) for reporting this issue.

## Which versions are affected by RUSTSEC-2026-0340?

1 open source package ship an affected version, including quinn-proto.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `quinn-proto` | crates.io | From 0.11.0 | 0.11.18 |

## How do I fix RUSTSEC-2026-0340?

Upgrade quinn-proto to 0.11.18 or later.

## Is RUSTSEC-2026-0340 being exploited?

There is no known exploitation of RUSTSEC-2026-0340 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0340 and fix it if it is affected.

What it is: RUSTSEC-2026-0340 is a denial of service vulnerability in quinn-proto, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of RUSTSEC-2026-0340 in the wild and no public exploit code.

Affected packages and fixed versions:
- quinn-proto (crates.io): affected from 0.11.0; fixed in 0.11.18

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-2026-0340/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0340/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0340

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0340/
Summaries are generated and may contain mistakes; the official description above is the record.