# CVE-2026-101276: iperf3 heap use-after-free in server watchdog timer

Source: https://junglewise.ai/threats/cve-2026-101276-iperf3-3-21-esnet-iperf-contains-a-remote-unauthenticated-heap  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-30. Updated: 2026-09-30  
License: CC BY 4.0 with a link back

CVE-2026-101276 · Severity: info · Published 2026-09-30

iperf3 is a network performance testing tool widely used by network operators to measure bandwidth. A flaw in version 3.21 allows a remote attacker to trigger a heap use-after-free vulnerability by connecting to the server, potentially causing crashes or enabling arbitrary code execution. The vulnerability has been patched in version 3.22.

Technologies: [ESnet Iperf3](https://junglewise.ai/threats/technologies/esnet-iperf3). Vendors: [ESnet](https://junglewise.ai/threats/vendors/esnet).

## Quick answers

**Is CVE-2026-101276 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101276 being exploited in the wild.

**How severe is CVE-2026-101276?** Informational severity, published 30 September 2026.

**Which products and versions are affected?** ESnet Iperf3 3.21.

**Is there a fix for CVE-2026-101276?** A patch was published on 2026-09-29: fixed in version 3.22 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-101276 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-101276?** Check whether you run ESnet Iperf3 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The server_timer_proc() watchdog function frees stream structures without properly cancelling or joining their associated worker threads, allowing blocked workers to dereference freed memory. This is a remote, unauthenticated heap use-after-free vulnerability accessible over the network. The fix in 3.22 ensures proper thread synchronization before freeing stream resources.

## Affected products

- esnet iperf3 3.21

## Timeline

- 2026-09-30: disclosed
- 2026-09-29: patched: fixed in version 3.22

## References

- [https://newreleases.io/project/github/esnet/iperf/release/3.22](https://newreleases.io/project/github/esnet/iperf/release/3.22)

## Related threats

- [iperf3 heap buffer overflow in RSA decryption](https://junglewise.ai/threats/cve-2026-101283-iperf3-3-20-3-21-esnet-iperf-has-a-pre-auth-heap-buffer-overflow)
- [iperf3 denial of service in UDP receive worker](https://junglewise.ai/threats/cve-2026-102253-iperf3-versions-prior-to-3-22-contains-a-denial-of-service)