CVE-2026-102253 in iperf3
Summary
by MITRE • 09/30/2026
iperf3 versions prior to 3.22 contains a denial of service vulnerability that allows unauthenticated remote attackers to crash-loop the server's UDP receive worker into an unrecoverable infinite loop by sending a single crafted control-channel parameter message followed by one 16-byte UDP datagram. Attackers can permanently pin the affected per-stream receive thread at approximately 100% CPU usage, rendering the server unusable until forcibly killed with SIGKILL, as the process does not respond to normal control-channel closure.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in iperf3 versions prior to 3.22 represents a critical denial of service flaw within the application's UDP receive worker logic. This issue stems from an improper handling of control channel parameters when processing incoming network traffic, specifically affecting the server-side components responsible for managing high-throughput data streams. The root cause lies in the failure of the software to correctly validate or terminate specific sequences of messages sent over the control channel followed by subsequent user datagram protocol packets. This architectural weakness allows an unauthenticated remote attacker to exploit the state machine governing the receive worker, forcing it into a pathological condition that prevents normal operation recovery without external intervention.
The technical mechanism of this exploitation involves a precise two-step sequence designed to trigger the infinite loop within the per-stream receive thread. First, the attacker sends a crafted control-channel parameter message that manipulates internal variables or flags related to stream management. Immediately following this initial packet, the attacker transmits a single 16-byte UDP datagram. This specific combination causes the server's processing logic to enter an unrecoverable infinite loop. Unlike typical denial of service attacks that consume bandwidth or memory resources gradually, this vulnerability results in immediate and sustained CPU saturation. The affected thread becomes permanently pinned at approximately one hundred percent CPU usage, effectively halting all other operations associated with that stream and potentially impacting the stability of the broader server environment depending on resource allocation policies.
The operational impact of this vulnerability is severe due to its persistence and resistance to standard recovery mechanisms. Once triggered, the compromised process does not respond to normal control-channel closure signals or graceful shutdown requests initiated by legitimate clients or administrators. This lack of responsiveness means that the denial of service condition persists until an external force intervenes. System administrators are forced to manually terminate the affected iperf3 server process using a SIGKILL signal, which abruptly stops execution but does not resolve the underlying code defect. Consequently, any services relying on this instance for performance testing or network analysis become unavailable during the incident window, leading to significant downtime and potential data loss if active transfers are interrupted without proper cleanup procedures.
From a classification perspective, this vulnerability aligns with CWE-835, which describes loops that consume excessive resources such as CPU time, often referred to as an infinite loop condition. It also maps closely to ATT&CK technique T1499, specifically Endpoint Denial of Service via resource exhaustion or service disruption. The attack vector is classified under Remote Code Execution principles in the context of availability impact, though technically it constitutes a remote denial of service rather than code execution. The unauthenticated nature of the exploit means that no prior access credentials are required to initiate the attack, significantly lowering the barrier for entry and increasing the risk profile for any publicly accessible iperf3 instances or those exposed within trusted networks without adequate segmentation.
Mitigation strategies must focus on immediate version upgrades and network-level controls. The primary remediation is to upgrade iperf3 to version 3.22 or later, where this specific logic flaw in the UDP receive worker has been addressed by developers through improved input validation and state machine corrections. In environments where upgrading is not immediately feasible, deploying a Web Application Firewall or intrusion prevention system capable of inspecting control channel payloads may help block the crafted parameter messages before they reach the vulnerable application layer. Additionally, implementing rate limiting on incoming connections can reduce the likelihood of successful exploitation by restricting the volume of packets an unauthenticated source can send in a short timeframe. Regular monitoring for abnormal CPU usage spikes associated with iperf3 processes should also be established to detect potential attempts or ongoing attacks early.