CVE-2025-24356
HIGHDescription
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.
How to fix
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Exploit Intelligence
Moderate risk: more likely to be exploited than 47% of all known CVEs.
References
Related Vulnerabilities
Other CWE-405 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2019-11479 | High | 7.5 | 92% | - | Fix |
| CVE-2024-11187 | High | 7.5 | 15% | - | Fix |
| CVE-2025-8677 | High | 7.5 | 11% | - | Fix |
| CVE-2021-38447 | High | 8.6 | 2.1% | - | Fix |
| CVE-2021-21359 | Medium | 5.9 | 1.7% | - | Fix |
| CVE-2018-15492 | High | 7.5 | 1.2% | - | - |
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-08-27.