CVE-2025-24356: 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…

PriorityP342high7.5CVSS 3.1

AVNACLPRNUINSUCNINAH

EPSS

0.65%

47.4th percentile

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.

Affected

5 ranges

Vendor	Product	Version range	Fixed in
debian	fastd	< fastd 23-1 (forky)	fastd 23-1 (forky)
fastd_project	fastd	< 23.0	23.0
fastd_project	fastd	>= 0 < 23-1	23-1
fastd_project	fastd	>= 0 < 23-1	23-1
neocturne	fastd	< 23	23

CVSS provenance

nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvdv4.06.9MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

osv6.9MEDIUM

vendor_debian6.9MEDIUM

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