Real OpenSSH doesn't log attempted passwords — only success/failure
with username — leaving SSH the sole auth-bearing service in the
fleet that contributes nothing to the cred corpus FTP/MySQL/RDP/
VNC/etc. populate. Closes that gap with a tiny pam_exec shim.
A static C helper (~80 LoC, musl, ~38KB stripped) is wired into
/etc/pam.d/sshd as `auth optional pam_exec.so expose_authtok stdout
/usr/sbin/auth-helper`. pam_exec writes the attempted password to
the helper's stdin NUL-terminated; the helper formats an RFC 5424
line in the exact shape templates/syslog_bridge.py produces
(facility local0, PEN 55555, MSGID auth_attempt — same MSGID FTP
uses) and writes it to /proc/1/fd/1 so the existing collector
stdout-reader pipeline picks it up.
Two password fields ride in the SD-block:
- password= RFC 5424 escaped, ASCII-printable only, ? for non-
printables. FTP-compatible — existing dashboard
rendering picks up SSH attempts unchanged.
- password_b64= base64 of the exact PAM_AUTHTOK bytes. Preserves
NUL/0xff/control-byte fingerprinting signal that the
plain field necessarily drops.
Fail-open by design: the PAM line is `optional` so a malfunctioning
helper never blocks sshd auth. Better to miss a cred than break the
honeypot.
Verified end-to-end inside the rebuilt image:
- 38KB static ELF, runs without a dynamic linker
- correct RFC 5424 line for `hunter2` → b64 `aHVudGVyMg==`
- NUL truncation matches pam_exec's contract
- 0xff bytes survive losslessly through password_b64
- empty password produces a well-formed line (e.g. pubkey auth path)
anti
d064125f61