# RUSTSEC-2026-0300: Use-after-free in `clear` and `retain` when an element's `Drop` panics

> A use-after-free and double-free vulnerability in the Rust SkipList library allows attackers to execute arbitrary code or cause denial of service if element Drop panics.

- **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:** 2 Sep 2026
- **Also known as:** GHSA-x6j6-3ffp-qrfr

## What is RUSTSEC-2026-0300?

RUSTSEC-2026-0300 is an use after free vulnerability in skiplist, published on 2 Sep 2026. 

### Official description

`SkipList::clear` drops the node chain and only then resets `tail` and `len`.
The drop runs each element's `Drop`, and `T` carries no bounds excluding a
panicking one. If it unwinds, `tail` still points at the freed node while `len`
stays non-zero.

`back()`, `back_mut()`, `last_key_value()` and `last()` dereference `tail`
through `unsafe`, so reading the container after the unwind is a use-after-free
(CWE-416). `Drop for SkipList` calls `Box::from_raw` on `self.head`, which
`clear` already destroyed, so dropping the container is a double free
(CWE-415).

`retain`, `retain_mut` and `dedup_by` reach the same state through
`Node::filter_rebuild`, which frees nodes and runs a user predicate before the
caller commits `tail` and `len`. There the head links are left partially
rewired, so traversal can also reach freed nodes.

## Mitigation

Update to 1.1.1.

## Which versions are affected by RUSTSEC-2026-0300?

1 open source package ship an affected version, including skiplist.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `skiplist` | crates.io | From 0.0.0-0 | 1.1.1 |

## How do I fix RUSTSEC-2026-0300?

Upgrade skiplist to 1.1.1 or later.

## Is RUSTSEC-2026-0300 being exploited?

There is no known exploitation of RUSTSEC-2026-0300 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for RUSTSEC-2026-0300 and fix it if it is affected.

What it is: RUSTSEC-2026-0300 is an use after free vulnerability in skiplist, published on 2 Sep 2026. 
Exploitation: There is no known exploitation of RUSTSEC-2026-0300 in the wild and no public exploit code.

Affected packages and fixed versions:
- skiplist (crates.io): affected from 0.0.0-0; fixed in 1.1.1

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-2026-0300/ (Markdown: https://insights.sbomify.com/RUSTSEC-2026-0300/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/RUSTSEC-2026-0300

---
From sbomify Insights: https://insights.sbomify.com/RUSTSEC-2026-0300/
Summaries are generated and may contain mistakes; the official description above is the record.