CVE-2025-24356: fastd is a VPN daemon which tunnels IP packets and Ethernet frames over UDP

Q: How do I fix CVE-2025-24356?

fastd: upgrade to 23.0. Exact commands for each OS are on this page.

Q: Is CVE-2025-24356 being exploited?

CVE-2025-24356 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-24356 affect?

CVE-2025-24356 affects fastd. Severity is high (CVSS 7.5). 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

Q: How urgent is CVE-2025-24356?

Priority 44/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2025-24356 is a high-severity flaw (CVSS 7.5) affecting fastd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 fas

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 48%)
CISA exploited list	No
Weakness	CWE-405
Published	2025-01-27
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: fastd project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-01-27 18:15 UTCPublished CVE record published
2026-06-17 08:58 UTCUpdated Record last modified

fastd project fastd UPGRADE

Affected: < 23.0

Fixed in: 23.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy fastd || rpm -q fastd || fastd --version

2. UPGRADE to 23.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fastd

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fastd

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-24356?

fastd: upgrade to 23.0. Exact commands for each OS are on this page.

Is CVE-2025-24356 being exploited?

CVE-2025-24356 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-24356 affect?

CVE-2025-24356 affects fastd. Severity is high (CVSS 7.5). 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

How urgent is CVE-2025-24356?

Priority 44/100. High severity; Remotely exploitable, no login, no user action

References

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