CVE-2026-92698 in FastNetMon
Summary
by MITRE • 11/06/2026
FastNetMon is a high-performance DDoS detector and sensor. In version 1.2.9 and earlier, process_sflow_flow_sample() in src/sflow_plugin/sflow_collector.cpp passes the attacker-controlled sflow_raw_protocol_header_t.header_size to parse_raw_packet_to_simple_packet_full() as its trusted captured length without comparing it with the bytes remaining in the record. An inflated header_size creates a false end pointer beyond the received sFlow v5 UDP buffer, defeating the nested parser's bounds checks and causing an unauthenticated remote out-of-bounds read and process crash, with possible limited exposure of adjacent bytes through parsed flow fields. No fixed release is available as of this review.
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Analysis
by VulDB Data Team • 11/06/2026
FastNetMon serves as a high-performance distributed denial of service detector and sensor, designed to monitor network traffic for malicious patterns such as volumetric attacks or application-layer exploits. The software relies on various protocols to collect telemetry data from routers and switches, including sFlow version 5, which is widely used in enterprise networks for flow sampling and monitoring. Within the architecture of FastNetMon, the component responsible for processing these samples resides in the source file src/sflow_plugin/sflow_collector.cpp. Specifically, the function process_sflow_flow_sample() handles incoming sFlow data streams to extract relevant metrics that trigger alerts or logging mechanisms. This module is critical because it processes untrusted network traffic directly from potentially compromised or misconfigured devices within the monitored infrastructure.
A critical vulnerability exists in versions 1.2.9 and earlier of FastNetMon, classified as an out-of-bounds read resulting from improper input validation. The technical flaw lies in how the application handles the header_size field contained within the sflow_raw_protocol_header_t structure received via UDP packets. When a sample is processed, this function passes the attacker-controlled value of header_size directly to parse_raw_packet_to_simple_packet_full() as the trusted captured length for parsing operations. Crucially, the code fails to compare this declared size against the actual number of bytes remaining in the sFlow v5 UDP buffer record. This lack of boundary verification allows an adversary who can inject or manipulate network traffic destined for FastNetMon to specify a header_size value that exceeds the available data payload.
The operational impact of this vulnerability is severe, leading primarily to service disruption through process crashes. By inflating the header_size field beyond the actual buffer limits, the application creates a false end pointer that extends past the allocated memory region containing the received sFlow packet. This action effectively defeats the nested parser's internal bounds checks, which rely on accurate length indicators to prevent reading outside valid memory segments. Consequently, when the parser attempts to access data at these invalid addresses, it triggers an out-of-bounds read condition. In most standard execution environments, this results in a segmentation fault or similar exception that causes the FastNetMon process to terminate abruptly. This denial of service effect undermines the reliability of the DDoS detection system, potentially leaving networks unprotected during active attacks if the monitoring service cannot recover automatically.
Beyond immediate availability issues, there is a secondary risk involving information disclosure. The out-of-bounds read may allow an attacker to expose adjacent bytes from memory that lie immediately after the intended sFlow buffer boundary. While the primary vector described focuses on crashing the process, improper handling of these extra bytes could theoretically lead to limited exposure of sensitive data residing in nearby memory locations through parsed flow fields or error messages returned by the application. This aspect aligns with CWE-125, which defines out-of-bounds read vulnerabilities where software reads past the end of a buffer, potentially leading to information leakage or system instability. The vulnerability is also relevant to MITRE ATT&CK technique T1498, Network Denial of Service, as it enables an unauthenticated remote actor to disrupt security monitoring capabilities by crashing the detection engine.
Mitigation strategies for this issue are currently constrained by the absence of a fixed software release as of the review period. Administrators relying on FastNetMon versions prior to 1.2.9 must implement compensating controls at the network perimeter. The most effective immediate mitigation is to restrict UDP traffic destined for the sFlow collector port to only trusted management networks or specific source IP addresses known to be legitimate flow exporters. Access control lists should be configured on upstream routers and firewalls to drop any sFlow packets originating from untrusted sources, thereby preventing malicious actors from sending crafted payloads that exploit this parsing flaw. Additionally, deploying network intrusion detection systems capable of identifying anomalous UDP packet sizes or malformed protocol headers can provide an additional layer of defense by filtering out suspicious traffic before it reaches the FastNetMon application. Organizations should also monitor system logs for frequent process restarts or segmentation faults associated with sFlow processing as indicators of potential exploitation attempts until a patched version is officially released and deployed.