Vulnerability in Fastd Project
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 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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.007 (51.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 51.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000
Affected products
- Fastd Project
- Neocturne Fastd — versions < 23
Weakness classification (CWE)
References
- github.com/neocturne/fastd/security/advisories/GHSA-pggg-vpfv-4rcv (Patch, Mitigation, Vendor Advisory)
- github.com/neocturne/fastd/commit/1f233bee76b722c0b3f9024f2c39c72e9f7e5843 (Patch)
- github.com/neocturne/fastd/commit/3940150e801d0c91460491bec32cbcc5bbc89d5f (Patch)
- github.com/neocturne/fastd/commit/5f63fcfc18ae9cad023fa463b152d5e14192b5a8 (Patch)
- github.com/neocturne/fastd/commit/9df7e516378441d2d17b89f9db5c27c8312d8f12 (Patch)
- github.com/neocturne/fastd/commit/c1a07b3f2b9066c3713c68547da700b85d60f4f7 (Patch)
- github.com/neocturne/fastd/commit/ce1b79b12dbfa796743b5f3a50789ade965b7023 (Patch)
- github.com/neocturne/fastd/commit/d03a0a17347efb5293e42fde7d982781e90f14ef (Patch)
Frequently asked questions
- What is CVE-2025-24356?
- CVE-2025-24356 is a high-severity vulnerability in Fastd Project, classified under Asymmetric Resource Consumption (Amplification). CVSS score: 7.5/10. Published 2025-01-27.
- How severe is CVE-2025-24356?
- High severity. CVSS v3 base score is 7.5 out of 10.