# CVE-2026-71218: iperf3 unbounded memory allocation in JSON_read

Source: https://junglewise.ai/threats/cve-2026-71218-iperf3-unbounded-memory-allocation-in-json-read  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-11. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-71218 · Severity: medium · CVSS 5.3 · Published 2026-08-11

iperf3 is a network bandwidth measurement tool widely used for testing network performance. A remote attacker can crash the iperf3 service by sending specially crafted messages that trigger unlimited memory allocation, causing the application to exhaust available system memory and become unavailable.

## Quick answers

**Is CVE-2026-71218 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-71218 being exploited in the wild.

**How severe is CVE-2026-71218?** Medium severity, with a CVSS score of 5.3, published 11 August 2026.

**Which products and versions are affected?** ESnet iperf3 <unknown.

**Is there a fix for CVE-2026-71218?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-71218 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-71218?** Check whether anything you run is named in the advisory. 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 vulnerability exists in the JSON_read() function, which accepts a peer-controlled message length parameter and allocates memory without enforcing an upper bound (CWE-789). An unauthenticated remote attacker can exploit this over the network by sending messages with artificially large length values, triggering excessive memory consumption before any authentication checks occur. This results in Denial of Service through memory exhaustion, severe slowdown, or termination of the iperf3 service. Mitigation includes restricting network access to the iperf3 control port and enforcing process-level memory limits; a patch has been released in upstream iperf3 (commit 0128d0357b7e8916fe39e980e455729bc0e5fd4e).

## Affected products

- ESnet iperf3 <unknown

## Timeline

- 2026-08-11: disclosed

## References

- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-71218](https://access.redhat.com/security/cve/CVE-2026-71218)