CVE catalog
CVE-2025-24356
fastd: CVE-2025-24356
- Severity
- Medium
- Published
- Source
- [NVD] · [CVE record]
- EPSS
- 0.68% · Oct 25, 2026
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.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | fastd | sid | 23-2 | fixed |
| Debian | fastd | forky | 23-2 | fixed |
| Debian | fastd | trixie | 23-2 | fixed |
| Debian | fastd | bookworm | 22-4 | vulnerable |
| Ubuntu | fastd | 16.04 | 17-4 | vulnerable |
| Ubuntu | fastd | 16.04 | 17-4build1 | vulnerable |
| Ubuntu | fastd | 16.04 | 17-4ubuntu0.1 | vulnerable |
| Ubuntu | fastd | 18.04 | 18-2 | vulnerable |
| Ubuntu | fastd | 18.04 | 18-2ubuntu1 | vulnerable |
| Ubuntu | fastd | 18.04 | 18-2ubuntu2 | vulnerable |
| Ubuntu | fastd | 18.04 | 18-3 | vulnerable |
| Ubuntu | fastd | 18.04 | 18-3ubuntu0.18.04.1 | vulnerable |
| Ubuntu | fastd | 20.04 | 18-3build1 | vulnerable |
| Ubuntu | fastd | 20.04 | 18-3ubuntu0.1 | vulnerable |
| Ubuntu | fastd | 22.04 | 21-1 | vulnerable |
| Ubuntu | fastd | 22.04 | 22-2 | vulnerable |
| Ubuntu | fastd | 22.04 | 22-2build1 | vulnerable |
| Ubuntu | fastd | 24.04 | 22-4 | vulnerable |
| Ubuntu | fastd | 24.04 | 22-4build1 | vulnerable |
| Ubuntu | fastd | 24.04 | 22-4build2 | vulnerable |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | fastd | source | sid | 23-1 | not yet assigned | Not reported | Not reported |
| Debian | fastd | source | forky | 23-1 | not yet assigned | Not reported | Not reported |
| Debian | fastd | source | trixie | 23-1 | not yet assigned | Not reported | Not reported |
| Debian | fastd | source | bookworm | (unfixed) | not yet assigned | Not reported | Not reported |
Notes
[bookworm] fastd: Minor issue
OpenFactory catalog packages
[Debian 12 (Bookworm)]
- [fastd]Affected
Details (2)
22-4· amd64 · bookwormAffected
dsa · fastd · debian · bookworm; dsa · fastd · debian · 12
22-4· arm64 · bookwormAffected
dsa · fastd · debian · bookworm; dsa · fastd · debian · 12
- [fastd-doc]Affected
Source package: [fastd]
Details (2)
22-4· all · bookwormAffected
dsa · fastd · debian · bookworm; dsa · fastd · debian · 12
22-4· all · bookwormAffected
dsa · fastd · debian · bookworm; dsa · fastd · debian · 12
[Debian 13 (Trixie)]
- [fastd]Fixed
Details (2)
23-2· amd64 · trixieFixed · Fixed:
23-1dsa · fastd · debian · 13
23-2· arm64 · trixieFixed · Fixed:
23-1dsa · fastd · debian · 13
- [fastd-doc]Fixed
Source package: [fastd]
Details (2)
23-2· all · trixieFixed · Fixed:
23-1dsa · fastd · debian · 13
23-2· all · trixieFixed · Fixed:
23-1dsa · fastd · debian · 13
Observed: