{"id":"CVE-2025-24356","aliases":["DEBIAN-CVE-2025-24356","EUVD-2025-3677","GHSA-pggg-vpfv-4rcv","UBUNTU-CVE-2025-24356"],"status":"published","title":"UDP traffic amplification via fastd's fast reconnect feature","description":"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":{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00708,"percentile":0.53805,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-405"],"published":"2025-01-27T17:31:38Z","modified":"2026-10-28T10:59:23Z","fixes":[{"ecosystem":"Debian:13","package":"fastd","fixed_in":["23-1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"fastd","fixed_in":["23-1"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:12","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["22-4","23-1","23-2"]},{"source":"osv","ecosystem":"Debian:13","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"23-1"}]}]},{"source":"osv","ecosystem":"Debian:14","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"23-1"}]}]},{"source":"osv","ecosystem":"Ubuntu:16.04:LTS","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["17-4","17-4build1","17-4ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["18-2","18-2ubuntu1","18-2ubuntu2","18-3","18-3ubuntu0.18.04.1"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["18-3build1","18-3ubuntu0.1"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["21-1","22-2","22-2build1"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"fastd","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["22-4","22-4build1","22-4build2"]}],"products":[{"vendor":"fastd_project","product":"fastd"},{"vendor":"neocturne","product":"fastd"}],"references":[{"url":"https://github.com/neocturne/fastd/security/advisories/GHSA-pggg-vpfv-4rcv","tags":["x_refsource_CONFIRM","Mitigation","Patch","Vendor Advisory","advisory","report"]},{"url":"https://github.com/neocturne/fastd/commit/1f233bee76b722c0b3f9024f2c39c72e9f7e5843","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/3940150e801d0c91460491bec32cbcc5bbc89d5f","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/5f63fcfc18ae9cad023fa463b152d5e14192b5a8","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/9df7e516378441d2d17b89f9db5c27c8312d8f12","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/c1a07b3f2b9066c3713c68547da700b85d60f4f7","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/ce1b79b12dbfa796743b5f3a50789ade965b7023","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/neocturne/fastd/commit/d03a0a17347efb5293e42fde7d982781e90f14ef","tags":["x_refsource_MISC","Patch","fix","report"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/24xxx/CVE-2025-24356.json","tags":["advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-24356","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2025-24356","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2025-24356","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2025-24356","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2025-24356","title":"UDP traffic amplification via fastd's fast reconnect feature","description":"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.","status":"published","published":"2025-01-27T17:31:38.541Z","modified":"2025-01-28T15:39:06.688Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L","level":"medium","assessor":"cna"}],"cwes":["CWE-405"],"updated_at":"2026-11-02T14:32:43.770144Z"}],"euvd":[{"id":"EUVD-2025-3677","description":"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.","status":"published","published":"2025-01-27T17:31:38Z","modified":"2025-01-28T15:39:06Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L","level":"medium"}],"updated_at":"2026-11-03T00:04:11.814906Z"}],"nvd":[{"id":"CVE-2025-24356","description":"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.","status":"published","published":"2025-01-27T18:15:41.347Z","modified":"2026-06-17T08:58:37.75Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS: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","level":"medium","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"}],"cwes":["CWE-405"],"updated_at":"2026-11-02T14:10:49.841519Z"}],"osv":[{"id":"CVE-2025-24356","title":"UDP traffic amplification via fastd's fast reconnect feature","description":"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.","status":"published","published":"2025-01-27T17:31:38.541Z","modified":"2026-10-28T10:59:23.350344856Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L","level":"medium"}],"cwes":["CWE-405"],"updated_at":"2026-11-02T15:44:47.009967Z"},{"id":"DEBIAN-CVE-2025-24356","description":"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.","status":"published","published":"2025-01-27T18:15:41.347Z","modified":"2026-09-01T20:05:45.007203788Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T15:45:45.870237Z"},{"id":"UBUNTU-CVE-2025-24356","description":"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.","status":"published","published":"2025-01-27T18:15:00Z","modified":"2025-10-24T05:18:08Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L","level":"medium"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T16:55:26.330196Z"}]}}