# CVE-2026-101276: Use after free in iperf3

> Remote unauthenticated attackers can trigger a heap use-after-free in iperf3 server, potentially leading to code execution or denial of service.

- **Severity:** Critical 9.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 30 Sep 2026
- **Updated:** 1 Oct 2026
- **Also known as:** AZL-105492, BELL-CVE-2026-101276, DEBIAN-CVE-2026-101276, GHSA-pmgg-x2vj-36cv, UBUNTU-CVE-2026-101276

## What is CVE-2026-101276?

CVE-2026-101276 is a critical use after free vulnerability in esnet iperf3, published on 30 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

iperf3 3.21 (esnet/iperf) contains a remote, unauthenticated heap use-after-free: the server's per-test watchdog server_timer_proc() frees streams without cancelling/joining their worker threads, so a blocked worker dereferences a freed iperf_stream; fixed in 3.22.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-101276?


## How do I fix CVE-2026-101276?

Upgrade to a fixed version.

## Is CVE-2026-101276 being exploited?

There is no known exploitation of CVE-2026-101276 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-101276 and fix it if it is affected.

What it is: CVE-2026-101276 is a critical use after free vulnerability in esnet iperf3, published on 30 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-2026-101276 in the wild and no public exploit code.

Affected product: esnet iperf3. 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-2026-101276/ (Markdown: https://insights.sbomify.com/CVE-2026-101276/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-101276
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-101276
- OSV: https://osv.dev/vulnerability/CVE-2026-101276

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-101276/
Summaries are generated and may contain mistakes; the official description above is the record.