CVE-2026-92694 in FastNetMon
Summary
by MITRE • 11/06/2026
FastNetMon is a high-performance DDoS detector and sensor. In version 1.2.9 and earlier, FastNetMon's IPv6 top-talkers screen-draw thread in draw_table_ipv6() in src/fastnetmon_logic.cpp iterates ipv6_host_counters.average_speed_map without holding counter_map_mutex while recalculate_speed() inserts new keys and may rehash the same map. The race requires networks_list to include the targeted IPv6 range. It causes confirmed undefined behavior under load; a process crash is plausible but was not observed, so reliable denial of service has not been established. 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 detection and sensor system designed to monitor network traffic patterns in real-time environments. The vulnerability identified affects versions 1.2.9 and earlier, specifically within the IPv6 top-talkers screen-draw functionality implemented in the draw_table_ipv6 function located in src/fastnetmon_logic.cpp. This component is responsible for rendering statistical data regarding IP addresses that generate the most traffic on an IPv6 network segment. The core technical flaw resides in a concurrency management failure where the thread handling the visual representation of this data accesses shared memory structures without proper synchronization mechanisms. Specifically, the function iterates over the average_speed_map contained within ipv6_host_counters while failing to acquire counter_map_mutex. This lack of mutual exclusion creates a critical race condition against concurrent operations performed by other threads, particularly those invoking recalculate_speed which is responsible for updating traffic metrics and potentially rehashing the underlying hash map structure.
The operational impact of this vulnerability stems from the fundamental principles of C++ standard library containers when subjected to unsynchronized modification during iteration. When one thread iterates over a std::map or similar associative container while another thread inserts new keys, the internal rebalancing or rehashing operations can invalidate iterators used by the reading thread. This scenario leads to undefined behavior as defined by the language specification. In practical terms within a production environment under heavy load, this race condition manifests as data corruption, incorrect statistical reporting, or most critically, application instability. While a confirmed reliable denial of service has not been established due to the probabilistic nature of race conditions and specific network configurations required, the potential for process crashes remains significant. The vulnerability requires that networks_list includes the targeted IPv6 range, meaning it is exploitable only in environments actively monitoring such traffic patterns with sufficient volume to trigger concurrent map modifications during screen updates.
From a security classification perspective, this issue aligns closely with CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization, commonly known as a race condition. The lack of proper locking mechanisms allows multiple execution paths to interfere with each other's state, leading to unpredictable outcomes that can compromise the integrity and availability of the monitoring service. Furthermore, this vulnerability relates to ATT&CK technique T1498 Network Denial of Service, specifically in the context of resource exhaustion or application instability caused by internal software flaws rather than external attack traffic. Although FastNetMon is a defensive tool against DDoS attacks, its own susceptibility to denial-of-service via race conditions presents an ironic and dangerous operational risk for network administrators relying on it for visibility.
Mitigation strategies must focus on eliminating the concurrency flaw at the code level since no fixed release was available as of the review period. Developers should ensure that all access points to shared data structures like average_speed_map are protected by appropriate mutex locks or other synchronization primitives such as read-write locks if multiple readers are permitted but writers require exclusive access. Implementing a copy-on-read strategy could also isolate iteration from concurrent modifications, although this may introduce performance overhead in high-throughput scenarios. Until an official patch is released, operators should consider reducing the frequency of screen-draw operations or disabling the IPv6 top-talkers visualization feature if it is not strictly necessary for their monitoring requirements. Additionally, deploying FastNetMon behind a reverse proxy with strict rate limiting on administrative interface requests may reduce the likelihood of triggering the race condition by throttling concurrent access patterns that exacerbate the timing window.