# CVE-2026-91095: Use after free in proxygen

> A use-after-free vulnerability in proxygen's WebTransport stream handling allows attackers to potentially execute arbitrary code or cause denial of service.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **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-c3mh-7h6x-xh3f

## What is CVE-2026-91095?

CVE-2026-91095 is a medium-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, the HTTPTransaction::onWebTransportUniStream and HTTPTransaction::onWebTransportBidiStream APIs could return stream handles that the stream handler had already freed. HQSession then installed those handles as transport read callbacks, which could lead to use of freed memory.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-91095?


## How do I fix CVE-2026-91095?

No fix has been published for CVE-2026-91095 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91095 being exploited?

There is no known exploitation of CVE-2026-91095 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91095 and fix it if it is affected.

What it is: CVE-2026-91095 is a medium-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-2026-91095 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-2026-91095/ (Markdown: https://insights.sbomify.com/CVE-2026-91095/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91095
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91095
- OSV: https://osv.dev/vulnerability/CVE-2026-91095

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91095/
Summaries are generated and may contain mistakes; the official description above is the record.