CVE-2026-48692

Vulnerability

FastNetMon Community Edition through version 1.2.9 exposes a gRPC API server on port 50052 with no authentication mechanism [1]. In src/fastnetmon.cpp at line 477, the server is initialized with grpc::InsecureServerCredentials(), and a source code comment explicitly states: "Listen on the given address without any authentication mechanism" [1][4]. All RPC methods in src/api.cpp — including ExecuteBan, ExecuteUnBan, GetBanlist, and GetTotalTrafficCounters — perform no credential verification [1][3]. No TLS, API token, client certificate, or role-based access control is implemented [1]. The default bind address is localhost, but the attacker must have local network access; if the address is changed to 0.0.0.0, any network-adjacent attacker can reach the API [1].

Exploitation

An attacker with network access to the gRPC endpoint (port 50052) can call any RPC method without authentication [1]. Specifically, ExecuteBan triggers BGP route announcements that blackhole the specified IP addresses, and ExecuteUnBan withdraws those routes, potentially re-enabling a DDoS attack [1]. Both methods can also execute the configured notify script via popen() [1]. The attacker does not need any prior credentials or special system access; the only requirement is network connectivity to the exposed port [1]. The disclosure blog provides proof-of-concept code demonstrating that arbitrary bans and unbans can be issued [1].

Impact

Successful exploitation allows an attacker to: (1) cause denial of service by banning legitimate IP addresses, blackholing their traffic; (2) disable DDoS mitigation by unbanning active attack sources; and (3) achieve arbitrary command execution on the server if the notify script is invoked with attacker-controlled data through popen() [1]. The impact spans all three CIA pillars — availability, integrity, and confidentiality — with the attacker gaining full control over the mitigation system and potentially the underlying host [1]. No role separation exists between read-only monitoring actions and destructive administrative operations [1].

Mitigation

As of May 26, 2026, no vendor patch or fix has been released for FastNetMon Community Edition [1]. The vendor (FastNetMon LTD) was notified on April 25, 2026 but has not responded [1]. Users are advised to restrict network access to port 50052 using a firewall (e.g., iptables) to accept connections only from trusted management hosts, and to avoid changing the bind address from 127.0.0.1 to 0.0.0.0 [1]. No workaround exists within the application itself [1]. This vulnerability is not currently listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.