# RUSTSEC-2026-0343: Outgoing datagram buffer accounting can panic the sender in quinn-proto

> A double subtraction bug in quinn-proto causes integer underflow and panics, leading to denial of service when sending datagrams.

- **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-ppcp-v39w-8jq2

## What is RUSTSEC-2026-0343?

RUSTSEC-2026-0343 is a 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

The limit on memory used to buffer outgoing datagrams, introduced in 0.11.17, subtracted an
evicted datagram's size from the buffered byte counter twice when `Datagrams::send` was called
with `drop = true` (as `Connection::send_datagram` in the `quinn` crate does) while the buffer was
full. Under sustained eviction the counter drifts below its true value: debug builds panic with an
integer underflow, while release builds wrap the counter, drain the whole queue, and then panic on
a desynchronization check in a later `send` call. In `quinn`, this panic occurs while the
connection lock is held, poisoning it and causing a double panic (and thus an abort) when the
connection is dropped.

This can be triggered without a malicious peer, by an application that sends a burst of datagrams
and then idles. It can also be triggered by a peer that keeps the connection alive with PING frames
while withholding acknowledgements, so that the sender's congestion window stays closed and the
outgoing queue never drains. Applications that use `send_datagram_wait` are not affected.

Only 0.11.17 is affected; the flaw was corrected in 0.11.18 by removing the redundant subtraction.

Thanks to [@alexpyattaev](https://github.com/alexpyattaev) for reporting and
[@vcarus](https://github.com/vcarus) for fixing this issue.

## Which versions are affected by RUSTSEC-2026-0343?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `quinn-proto` | crates.io | From 0.11.17 | 0.11.18 |

## How do I fix RUSTSEC-2026-0343?

Upgrade quinn-proto to 0.11.18 or later.

## Is RUSTSEC-2026-0343 being exploited?

There is no known exploitation of RUSTSEC-2026-0343 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0343 and fix it if it is affected.

What it is: RUSTSEC-2026-0343 is a 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-2026-0343 in the wild and no public exploit code.

Affected packages and fixed versions:
- quinn-proto (crates.io): affected from 0.11.17; 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-2026-0343/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0343/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0343

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0343/
Summaries are generated and may contain mistakes; the official description above is the record.