iperf3: Use-after-free in server watchdog timer, unauthenticated remote access
Summary
A use-after-free flaw in the iperf3 server allows a remote, unauthenticated attacker to corrupt heap memory. The server's watchdog timer frees test streams without stopping their worker threads, so a blocked worker can access freed memory. The official CVE record describes the impact as high on confidentiality, integrity and availability, but the vendor's release notes assign a heap buffer overflow in iperf_auth.c to this CVE ID, so the exact scope is not yet confirmed.
Affected
- iperf3 3.21 (confirmed in the CNA record)
- Older versions: unknown, sources conflict and the vendor has not clarified.
Fixed in
- iperf 3.22, released 2026-09-29
- Distribution packages: check with the vendor; openSUSE and SUSE list 3.22-based packages.
Workaround
- No vendor-documented workaround.
- Until patched, restrict which hosts can reach iperf3 server ports with firewall rules.
- Do not run iperf3 servers on internet-facing systems.
- Stop the iperf3 server when it is not needed.
Exploitation
- No evidence of exploitation in the wild found in the sources reviewed.
- No public proof of concept found.
- CISA SSVC assessment: Exploitation none, Automatable no, Technical Impact total.
- NVD analysis was pending at the time of research.
Our recommendation
- Inventory all systems where iperf3 is installed, including as a library (libiperf) or inside appliances.
- Upgrade to iperf 3.22 or to the distribution package that contains the fix.
- Disable the iperf3 server where it is not required.
- Restrict server access to known management or test networks.
- Ask the vendor (iperf@es.net) to confirm the CVE assignment for the heap buffer overflow and use-after-free descriptions.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- esnet/iperf 3.22 release notes (NewReleases) newreleases.io
- iperf 3.22 release tag (GitHub) github.com
- VulDB CVE-2026-101276 vuldb.com
- Strix CVE-2026-101276 www.strix.ai
- OSV Debian CVE-2026-101276 osv.dev
- SUSE CVE-2026-101276 (Vulners) vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 05:01.
Original description (NVD)
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.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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