# CVE-2026-91096: Use after free in proxygen

> Attackers can trigger a use-after-free in proxygen's WebTransport implementation, potentially leading to code execution or crashes.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Sep 2026
- **Updated:** 30 Sep 2026
- **Also known as:** GHSA-8mv4-xrj3-xg7m

## What is CVE-2026-91096?

CVE-2026-91096 is a high-severity use after free vulnerability in Facebook proxygen, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In proxygen from v2024.10.28.00 until v2026.09.28.00, WebTransportImpl::terminateSessionStreams (WebTransportImpl::destroy in releases before v2025.08.18.00) failed to unregister read callbacks for streams that were no longer open before destroying them. The transport could then invoke a read callback that had been freed.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-91096?


## How do I fix CVE-2026-91096?

No fix has been published for CVE-2026-91096 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91096 being exploited?

There is no known exploitation of CVE-2026-91096 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91096 and fix it if it is affected.

What it is: CVE-2026-91096 is a high-severity use after free vulnerability in Facebook proxygen, published on 28 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 CVE-2026-91096 in the wild and no public exploit code.

Affected product: Facebook proxygen. No package-level version data is available, so check the vendor advisory linked from the reference page.

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/CVE-2026-91096/ (Markdown: https://insights.sbomify.com/CVE-2026-91096/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91096
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91096
- OSV: https://osv.dev/vulnerability/CVE-2026-91096

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91096/
Summaries are generated and may contain mistakes; the official description above is the record.