PT-2025-5339 · Fastd+1 · Fastd+1

Neocturne · Published 2025-01-26 · Updated 2025-08-27 · CVE-2025-24356

Positive Technologies (AI Summary)

CVSS v3.1

7.5

High

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Name of the Vulnerable Software and Affected Versions fastd versions prior to v23

Description fastd is a VPN daemon that tunnels IP packets and Ethernet frames over UDP. When receiving a data packet from an unknown IP address/port combination, fastd initiates a reconnect by sending a handshake packet. This "fast reconnect" avoids waiting for a session timeout until a new connection is established. Even a small UDP packet can trigger a larger handshake packet, resulting in a roughly 12-13 amplification factor. This amplification of UDP traffic could be used to facilitate a Distributed Denial of Service attack by sending data packets with a spoofed source address to fastd instances reachable on the internet.

Recommendations For fastd versions prior to v23, update to version v23 or later to resolve the issue. As a temporary workaround, consider restricting access to fastd instances to minimize the risk of exploitation. Avoid exposing fastd instances to the internet without proper security measures in place.

Exploit

Fix

DoS

Weakness Enumeration

CWE-405

Related Identifiers

BDU:2025-14006

CVE-2025-24356

GHSA-PGGG-VPFV-4RCV

Affected Products

Debian

Fastd

References · 21

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/24xxx/CVE-2025-24356.json · Exploit
• https://github.com/neocturne/fastd/commit/ce1b79b12dbfa796743b5f3a50789ade965b7023 · Patch
• https://github.com/neocturne/fastd/commit/1f233bee76b722c0b3f9024f2c39c72e9f7e5843 · Patch
• https://github.com/neocturne/fastd/commit/9df7e516378441d2d17b89f9db5c27c8312d8f12 · Patch
• https://github.com/neocturne/fastd/commit/5f63fcfc18ae9cad023fa463b152d5e14192b5a8 · Patch
• https://github.com/neocturne/fastd/commit/c1a07b3f2b9066c3713c68547da700b85d60f4f7 · Patch
• https://github.com/neocturne/fastd/commit/d03a0a17347efb5293e42fde7d982781e90f14ef · Patch
• https://github.com/neocturne/fastd/commit/3940150e801d0c91460491bec32cbcc5bbc89d5f · Patch
• https://github.com/neocturne/fastd/security/advisories/GHSA-pggg-vpfv-4rcv · Vendor Advisory
• https://bdu.fstec.ru/vul/2025-14006 · Security Note
• https://security-tracker.debian.org/tracker/CVE-2025-24356 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2025-24356 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2025-24356 · Security Note
• https://osv.dev/vulnerability/DEBIAN-CVE-2025-24356 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2025-24356 · Vendor Advisory