anti
cdbb3d3571
ANTI flagged two regressions in the existing command-event capture: 1. **Tell**: PROMPT_COMMAND lived in /root/.bashrc, the FIRST file an attacker greps after landing root. The logger invocation sitting there is plain-text honeypot signage. 2. **Bypass**: even when missed, `export PROMPT_COMMAND=""` silently disables capture. ANTI personally bypasses this on engagements. Reshape: * Move the assignment to **/etc/environment** — read by pam_env at session open (sshd via /etc/pam.d/sshd, telnet via /etc/pam.d/login), before any shell rc file fires. Far less obvious than .bashrc; a casual `cat .bashrc` no longer surfaces the capture. * Define the helper as a function `__bash_history_sync` in **/etc/bash.bashrc** (system-wide bashrc, sourced by every interactive bash). Function name reads as generic bash housekeeping; no DECNET branding in the symbol. * Pin both the function and PROMPT_COMMAND **readonly** so `export PROMPT_COMMAND=""` fails with "readonly variable" instead of silently winning. Mitigation, not airtight — `bash --norc` still bypasses — but the passive `export` bypass is closed. The actual `logger --rfc5424 --msgid command ... CMD ...` invocation is preserved exactly; only its location and the readonly guard change. R0001–R0030 (command-rule pack) consume the same syslog shape as before. Three new tests assert: the value lands in /etc/environment, the function body lives in /etc/bash.bashrc, no PROMPT_COMMAND line remains in /root/.bashrc, and `readonly PROMPT_COMMAND` / `readonly -f __bash_history_sync` are both present. Mirror assertions added on the Telnet Dockerfile via test_config_schema.py.
110 lines
5.0 KiB
Docker
110 lines
5.0 KiB
Docker
ARG BASE_IMAGE=debian:bookworm-slim
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# ── Stage 1: build the static auth-helper credential-capture binary ──────────
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# Same source the SSH template builds — generic over PAM service. Wired
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# into /etc/pam.d/login below so every busybox-telnetd → /bin/login auth
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# attempt is captured before pam_unix runs. Static + musl: ~38 KB ELF,
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# zero libc version coupling, runs anywhere.
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FROM debian:bookworm-slim AS auth-helper-build
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RUN apt-get update && apt-get install -y --no-install-recommends musl-tools \
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&& rm -rf /var/lib/apt/lists/*
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COPY auth-helper/auth-helper.c /tmp/auth-helper.c
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RUN musl-gcc -static -O2 -s -Wall -Wextra \
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-o /auth-helper /tmp/auth-helper.c
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# ── Stage 2: the actual telnet decky image ───────────────────────────────────
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FROM ${BASE_IMAGE}
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# `login` (real Debian /bin/login, PAM-aware) replaces busybox's PAM-less
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# login applet. libpam-modules ships pam_exec.so transitively. Both are
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# needed for the auth-helper hook to fire — without them the PAM stack
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# can't load pam_exec or call into a real PAM service.
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RUN apt-get update && apt-get install -y --no-install-recommends \
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busybox-static \
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login \
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libpam-modules \
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rsyslog \
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procps \
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net-tools \
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&& rm -rf /var/lib/apt/lists/*
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# sessrec (pty transcript recorder) becomes root's login shell so busybox
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# /bin/login exec's it after PAM auth. gcc + libc6-dev are installed only
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# for this compile step and purged in the same layer.
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COPY sessrec/ /tmp/build/sessrec/
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RUN set -eu \
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&& apt-get update \
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&& apt-get install -y --no-install-recommends gcc libc6-dev make \
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&& mkdir -p /usr/libexec \
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&& make -C /tmp/build/sessrec install PREFIX=/usr/libexec \
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&& grep -q '^/usr/libexec/login-session$' /etc/shells \
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|| echo '/usr/libexec/login-session' >> /etc/shells \
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&& sed -i 's|^root:\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):.*$|root:\1:\2:\3:\4:\5:/usr/libexec/login-session|' /etc/passwd \
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&& apt-get purge -y gcc libc6-dev make \
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&& apt-get autoremove -y \
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&& rm -rf /var/lib/apt/lists/* /tmp/build
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# rsyslog: forward auth.* and user.* to named pipe in RFC 5424 format
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RUN printf '%s\n' \
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'# syslog-relay log bridge — auth + user events → named pipe as RFC 5424' \
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'$template RFC5424fmt,"<%PRI%>1 %TIMESTAMP:::date-rfc3339% %HOSTNAME% %APP-NAME% %PROCID% %MSGID% %STRUCTURED-DATA% %msg%\n"' \
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'auth,authpriv.* |/run/systemd/journal/syslog-relay;RFC5424fmt' \
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'user.* |/run/systemd/journal/syslog-relay;RFC5424fmt' \
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> /etc/rsyslog.d/50-journal-forward.conf
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# Disable imklog — containers can't read /proc/kmsg
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RUN sed -i 's/^\(module(load="imklog"\)/# \1/' /etc/rsyslog.conf
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# Silence default catch-all rules
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RUN sed -i \
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-e 's|^\(\*\.\*;auth,authpriv\.none\)|#\1|' \
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-e 's|^auth,authpriv\.\*|#auth,authpriv.*|' \
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/etc/rsyslog.conf
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# auth-helper: drop the static binary into /usr/sbin and wire pam_exec
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# into the login PAM stack so every busybox-telnetd password attempt
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# (success or fail) is captured before pam_unix runs. Same `optional`
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# fail-open semantics as the SSH template.
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COPY --from=auth-helper-build /auth-helper /usr/sbin/auth-helper
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RUN chmod 755 /usr/sbin/auth-helper && \
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sed -i '1i auth optional pam_exec.so expose_authtok stdout /usr/sbin/auth-helper' \
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/etc/pam.d/login
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# Realistic motd and issue banner
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RUN echo "Ubuntu 20.04.6 LTS" > /etc/issue.net && \
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echo "Welcome to Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-150-generic x86_64)" > /etc/motd && \
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echo "" >> /etc/motd && \
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echo " * Documentation: https://help.ubuntu.com" >> /etc/motd
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# Fake lived-in files
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RUN mkdir -p /root/scripts /root/backups && \
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printf '#!/bin/bash\n# DB backup script\nmysqldump -u root -padmin prod_db > /root/backups/db.sql\n' > /root/scripts/backup.sh && \
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printf 'DB_HOST=10.0.0.5\nDB_USER=admin\nDB_PASS=changeme123\n' > /root/.env && \
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printf 'alias ll="ls -alF"\nalias la="ls -A"\nexport HISTSIZE=1000\n' >> /root/.bashrc
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# Command-event capture. PROMPT_COMMAND is set in /etc/environment
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# (read by pam_env at /bin/login session open, before any shell rc
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# fires) and pinned readonly via /etc/bash.bashrc — `export
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# PROMPT_COMMAND=""` fails with "readonly variable" instead of
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# silently disabling capture. Function name is generic so a casual
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# `set | grep PROMPT` doesn't surface DECNET branding.
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RUN printf 'PROMPT_COMMAND=__bash_history_sync\n' >> /etc/environment \
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&& printf '%s\n' \
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'# bash history → syslog, system-wide.' \
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'__bash_history_sync() {' \
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' logger --rfc5424 --msgid command -p user.info -t bash "CMD uid=$UID pwd=$PWD cmd=$(history 1 | sed '"'"'s/^ *[0-9]* *//'"'"')"' \
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'}' \
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'readonly -f __bash_history_sync 2>/dev/null || true' \
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'readonly PROMPT_COMMAND 2>/dev/null || true' \
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>> /etc/bash.bashrc
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COPY entrypoint.sh /entrypoint.sh
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RUN chmod +x /entrypoint.sh
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EXPOSE 23
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HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
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CMD kill -0 1 || exit 1
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ENTRYPOINT ["/entrypoint.sh"]
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