CVE-2025-24356

6.9 MEDIUM 0.7% exploit odds Fix listed Denial of service Network gear

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. Limited direct impact.
Exploit odds: 0.7% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2025-01-27 18:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-06-17 08:58 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.7% in the next 30 days (EPSS).
Severity: 6.9 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2025-01-27 18:15 UTC
Last modified: 2026-06-17 08:58 UTC
Exploit probability: 0.7% · EPSS, next 30 days
Weakness: CWE-405
Record status: Analyzed

Affected

Fastd Project Fastd < 23.0

Attack profile CVSS 4.0 · 6.9

Attack vector: Network
Complexity: Low
Attack requirements: None
Privileges needed: None
User interaction: None
Confidentiality: None
Integrity: None
Availability: None

Raw 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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2025-24356.md and follow it. Check whether this project is affected by CVE-2025-24356. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record