vcheck

README

vcheck

Audit a remote Linux host over SSH for the Copy Fail and Dirty Frag kernel-module vulnerabilities and, optionally, apply mitigations:

CVE	Name	Affected modules
CVE-2026-31431	Copy Fail	algif_aead
CVE-2026-43284	Dirty Frag (IPsec)	esp4, esp6, xfrm_algo, xfrm_user
CVE-2026-43500	Dirty Frag (RxRPC)	rxrpc, kafs

For each affected module, vcheck reports whether it is currently loaded, has past traces in kernel logs, has live AF_ALG sockets (Copy Fail only), and whether it is already blacklisted under /etc/modprobe.d/.

With -fix, vcheck writes a cve-XXXX-XXXXX-disable.conf snippet for any module that is not yet blacklisted, then re-runs the checks and reports the final state.

Installation

Homebrew (macOS):

brew install krisiasty/tap/vcheck

Pre-built binaries for Linux, macOS, and Windows are published on the releases page.

From source (requires Go 1.26+):

go install github.com/krisiasty/vcheck@latest

Usage

vcheck -host HOST [flags]

Flag	Default	Description
-host	(required)	Remote host
-user	$USER	Remote user
-port	22	Remote SSH port
-agent	true	Use SSH agent for authentication
-identity	(empty)	Path to a private key file (prompts for passphrase if encrypted)
-password	false	Prompt for an SSH password
-insecure	false	Accept host keys not yet recorded in known_hosts; mismatches with a recorded key still fail
-fix	false	Write /etc/modprobe.d snippets for modules that are not already blacklisted
-timeout	15s	SSH connect timeout
-debug	false	Increase log verbosity
-version	false	Show version and exit

At least one of -agent, -identity, or -password must produce a usable authentication method. Methods are tried in the order listed.

Sudo is required on the target. If passwordless sudo is configured the tool proceeds silently; otherwise it prompts once for a password (input is hidden) and feeds it via sudo -S for every subsequent command.

Exit codes

Code	Meaning
0	All affected modules mitigated (blacklisted, not loaded, no active exposure)
1	Usage error
2	SSH connection failed
3	Sudo authentication failed
4	One or more modules not blacklisted (no current exposure)
5	One or more modules currently loaded or actively in use
99	Internal/check failure

Sample output

Fully mitigated host

$ vcheck -host host.example.com -identity ~/.ssh/id_ed25519
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF mitigated cve=CVE-2026-31431 module=algif_aead
INF mitigated cve=CVE-2026-43284 module=esp4
INF mitigated cve=CVE-2026-43284 module=esp6
INF mitigated cve=CVE-2026-43284 module=xfrm_algo
INF mitigated cve=CVE-2026-43284 module=xfrm_user
INF mitigated cve=CVE-2026-43500 module=rxrpc
INF mitigated cve=CVE-2026-43500 module=kafs

Unmitigated and partially loaded — bare check

$ vcheck -host host.example.com -identity ~/.ssh/id_ed25519
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF mitigated cve=CVE-2026-31431 module=algif_aead
ERR VULNERABLE cve=CVE-2026-43284 module=esp4 loaded=true
ERR module not blacklisted cve=CVE-2026-43284 module=esp6
ERR module not blacklisted cve=CVE-2026-43284 module=xfrm_algo
ERR module not blacklisted cve=CVE-2026-43284 module=xfrm_user
ERR module not blacklisted cve=CVE-2026-43500 module=rxrpc
ERR module not blacklisted cve=CVE-2026-43500 module=kafs

Same host with -fix — first run

$ vcheck -fix -host host.example.com -identity ~/.ssh/id_ed25519
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF writing modprobe.d snippet path=/etc/modprobe.d/cve-2026-43284-disable.conf modules="[esp4 esp6 xfrm_algo xfrm_user]"
INF writing modprobe.d snippet path=/etc/modprobe.d/cve-2026-43500-disable.conf modules="[rxrpc kafs]"
INF re-scanning after fix snippets_written=2
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF mitigated cve=CVE-2026-31431 module=algif_aead
ERR blacklisted but currently loaded; run 'modprobe -r' or reboot cve=CVE-2026-43284 module=esp4
INF mitigated cve=CVE-2026-43284 module=esp6
INF mitigated cve=CVE-2026-43284 module=xfrm_algo
INF mitigated cve=CVE-2026-43284 module=xfrm_user
INF mitigated cve=CVE-2026-43500 module=rxrpc
INF mitigated cve=CVE-2026-43500 module=kafs

The blacklist is in place, but esp4 was already loaded into the kernel before the snippet was written. Reboot or run sudo modprobe -r esp4 on the target to fully clear it.

Second run — esp4 still loaded

$ vcheck -fix -host host.example.com -identity ~/.ssh/id_ed25519
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF fix: nothing to do — all affected modules already blacklisted
INF mitigated cve=CVE-2026-31431 module=algif_aead
ERR blacklisted but currently loaded; run 'modprobe -r' or reboot cve=CVE-2026-43284 module=esp4
INF mitigated cve=CVE-2026-43284 module=esp6
INF mitigated cve=CVE-2026-43284 module=xfrm_algo
INF mitigated cve=CVE-2026-43284 module=xfrm_user
INF mitigated cve=CVE-2026-43500 module=rxrpc
INF mitigated cve=CVE-2026-43500 module=kafs

Third run — after modprobe -r esp4

$ vcheck -host host.example.com -identity ~/.ssh/id_ed25519
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
INF checking vulnerability cve=CVE-2026-43284 name="Dirty Frag (IPsec)"
INF checking vulnerability cve=CVE-2026-43500 name="Dirty Frag (RxRPC)"
INF mitigated cve=CVE-2026-31431 module=algif_aead
INF mitigated cve=CVE-2026-43284 module=esp4
INF mitigated cve=CVE-2026-43284 module=esp6
INF mitigated cve=CVE-2026-43284 module=xfrm_algo
INF mitigated cve=CVE-2026-43284 module=xfrm_user
INF mitigated cve=CVE-2026-43500 module=rxrpc
INF mitigated cve=CVE-2026-43500 module=kafs

First-time host — -insecure

$ vcheck -insecure -host host.example.com -identity ~/.ssh/id_ed25519
WRN host key not in known_hosts; accepting due to -insecure host=host.example.com:22 remote=192.0.2.42:22 fingerprint=SHA256:AAAAEXAMPLEfingerPrint000000000000000000000
INF connected user=ops host=host.example.com port=22
INF checking vulnerability cve=CVE-2026-31431 name="Copy Fail"
...

-insecure accepts hosts that are not yet in known_hosts. If a host is already recorded and presents a different key, the connection still fails — the flag is only a "first contact" override, not a way to suppress man-in-the-middle warnings on a known host.

Detection details

• Loaded: lsmod is fetched once and module names are matched against the first column.
• Blacklisted: every file under /etc/modprobe.d/ is searched (grep -rE) for an install <module> /bin/false directive — the same form vcheck writes with -fix. Other forms of disabling (e.g. blacklist) are not recognized.
• Past activity: journalctl -k is consulted first, with a fallback to /var/log/kern.log; the last five matching lines per module are kept.
• Active sockets (algif_aead only): ss -p --af-alg lists open AF_ALG sockets; any output other than the header counts as live use.

All commands run via sudo — privileged access is required to read /var/log/kern.log, list AF_ALG sockets, and write under /etc/modprobe.d/.