CVE-2026-92697
Description
A flaw was found in FastNetMon. This vulnerability allows an unauthenticated remote attacker to cause a Denial of Service (DoS) by crashing the service. By sending specially crafted network packets containing unterminated data fields to the NetFlow collector, an attacker can trigger an out-of-bounds read error that abruptly terminates the monitoring process.
Statement
Red Hat rates this vulnerability as Important because an unauthenticated remote attacker can abruptly terminate the monitoring daemon without credentials, leading to a complete service disruption. This risk warrants an Important severity rating because disabling the network sensor blinds administrators to traffic anomalies and denial-of-service conditions, despite the flaw not facilitating code execution or data exposure. Impact is greatest in environments where the NetFlow collector port is exposed to wider network segments rather than restricted to authorized flow-exporting devices.
Mitigation
Restrict network exposure so only trusted network devices (such as designated flow-exporting routers and switches) can reach the NetFlow collector port, or disable the daemon if flow monitoring is not needed.
1. Restrict the NetFlow UDP port (default 2055) to trusted sources using firewalld:
firewall-cmd --permanent --zone=trusted --add-source=<ROUTER_IP>/32
firewall-cmd --permanent --zone=trusted --add-port=2055/udp
firewall-cmd --reload
2. Alternatively, disable the service entirely if NetFlow processing is not required:
systemctl stop fastnetmon
systemctl disable fastnetmon
Caveats:
Restricting UDP traffic mitigates untrusted external exploitation, but any flow exporter within the allowed IP range could still trigger the flaw if compromised or misconfigured. Stopping the daemon halts DDoS traffic detection and flow collection completely.
Warning: Modifying firewall rules requires reloading the firewalld configuration (`firewall-cmd --reload`), which immediately alters active packet filtering rules. Stopping the daemon interrupts active monitoring services.
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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