EUVD-2026-31845
GHSA-w743-79pp-vx63
Severity by source
AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
Lifecycle Timeline
3DescriptionNVD
FastNetMon Community Edition through 1.2.9 exposes a gRPC API server on port 50052 with no authentication mechanism. The server is initialized with grpc::InsecureServerCredentials() (src/fastnetmon.cpp line 477) and a source code comment explicitly acknowledges 'Listen on the given address without any authentication mechanism.' None of the RPC methods in src/api.cpp (ExecuteBan, ExecuteUnBan, GetBanlist, GetTotalTrafficCounters, etc.) perform any credential verification. The ExecuteBan and ExecuteUnBan methods trigger security-critical actions: BGP route announcements that can blackhole network traffic, and execution of external notification scripts via popen(). An attacker with local network access can ban arbitrary IP addresses (causing denial of service to legitimate traffic), unban active attacks (disabling DDoS mitigation), and trigger script execution. There is also no role-based access control separating read-only monitoring from destructive administrative operations.
AnalysisAI
Unauthenticated gRPC API exposure in FastNetMon Community Edition through 1.2.9 allows adjacent network attackers to invoke security-critical RPC methods including ExecuteBan and ExecuteUnBan without credentials. The server explicitly uses grpc::InsecureServerCredentials() on port 50052, enabling attackers to blackhole legitimate traffic via BGP announcements, disable active DDoS mitigations, and trigger external script execution via popen(). No public exploit identified at time of analysis, and EPSS is low at 0.03%, but CISA SSVC rates technical impact as total.
Technical ContextAI
FastNetMon is an open-source DDoS detection and mitigation tool that integrates with BGP routers to blackhole attack traffic. The vulnerable component is its gRPC management API implemented in src/api.cpp and bound in src/fastnetmon.cpp at line 477. The root cause is CWE-306 (Missing Authentication for Critical Function): the gRPC server is intentionally initialized with grpc::InsecureServerCredentials(), a transport-layer credentials option that disables TLS and authentication entirely, and none of the RPC handlers (ExecuteBan, ExecuteUnBan, GetBanlist, GetTotalTrafficCounters) perform any credential or role check. Because ExecuteBan/UnBan drive BGP route announcements and invoke popen() against notification scripts, the API directly exposes destructive network-control primitives to anyone able to reach TCP/50052.
RemediationAI
No vendor-released patch identified at time of analysis; the referenced GitHub links point only to the vulnerable source files, not to a tagged fix. As compensating controls, restrict TCP/50052 to localhost or a dedicated management VLAN using host firewall rules (iptables/nftables) or by binding the gRPC listener to 127.0.0.1 if a configuration option permits, which prevents adjacent-network abuse but breaks any remote orchestration that relies on the gRPC API; place the FastNetMon host behind a network ACL that allows only known operator workstations and automation systems to reach port 50052, accepting the operational cost of maintaining that allowlist; and where the gRPC API is not actively used, disable it entirely to remove the attack surface, at the cost of losing programmatic ban/unban control. Until upstream adds authentication, monitor for unexpected ExecuteBan/ExecuteUnBan invocations and alert on changes to the banlist via GetBanlist polling. Track upstream fixes at https://github.com/pavel-odintsov/fastnetmon and the analyst write-up at https://lorikeetsecurity.com/blog/fastnetmon-cve-2026-48692-grpc-no-auth.
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External POC / Exploit Code
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