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CVE-2025-24356
Date: January 27, 2025
fastd is a VPN daemon which tunnels IP packets and Ethernet frames over UDP. When receiving a data packet from an unknown IP address/port combination, fastd will assume that one of its connected peers has moved to a new address and initiate a reconnect by sending a handshake packet. This "fast reconnect" avoids having to wait for a session timeout (up to ~90s) until a new connection is established. Even a 1-byte UDP packet just containing the fastd packet type header can trigger a much larger handshake packet (~150 bytes of UDP payload). Including IPv4 and UDP headers, the resulting amplification factor is roughly 12-13. By sending data packets with a spoofed source address to fastd instances reachable on the internet, this amplification of UDP traffic might be used to facilitate a Distributed Denial of Service attack. This vulnerability is fixed in v23.
Severity Score
Related Resources (11)
Severity Score
Weakness Type (CWE)
Asymmetric Resource Consumption (Amplification)
CWE-405CVSS v3.1
Base Score: |
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Attack Vector (AV): | NETWORK |
Attack Complexity (AC): | LOW |
Privileges Required (PR): | NONE |
User Interaction (UI): | NONE |
Scope (S): | UNCHANGED |
Confidentiality (C): | NONE |
Integrity (I): | NONE |
Availability (A): | HIGH |