detection rules: YARA + Falco for the 6 highest-rank modules + playbook
Closes the 'rules in the box' gap — the README has claimed YARA + Falco coverage but detect_yara and detect_falco were NULL on every module. This commit lights up both formats for the 6 highest-value modules (covering 10 of 31 registered modules via family-shared rules), and the existing operational playbook gains the format-specific deployment recipes + the cross-format correlation table. YARA rules (8 rules, 9 module-headers, 152 lines): - copy_fail_family — etc_passwd_uid_flip + etc_passwd_root_no_password (shared across copy_fail / copy_fail_gcm / dirty_frag_esp / dirty_frag_esp6 / dirty_frag_rxrpc) - dirty_pipe — passwd UID flip pattern, dirty-pipe-specific tag - dirtydecrypt — 28-byte ELF prefix match on tiny_elf[] + setuid+execve shellcode tail, detects the page-cache overlay landing - fragnesia — 28-byte ELF prefix on shell_elf[] + setuid+setgid+seteuid cascade, detects the 192-byte page-cache overlay - pwnkit — gconv-modules cache file format (small text file with module UTF-8// X// /tmp/...) - pack2theroot — malicious .deb (ar archive + SUID-bash postinst) + /tmp/.suid_bash artifact scan Falco rules (13 rules, 9 module-headers, 219 lines): - pwnkit — pkexec with empty argv + GCONV_PATH/CHARSET env from non-root - copy_fail_family — AF_ALG socket from non-root + NETLINK_XFRM from unprivileged userns + /etc/passwd modified by non-root - dirty_pipe — splice() of setuid/credential file by non-root - dirtydecrypt — AF_RXRPC socket + add_key(rxrpc) by non-root - fragnesia — TCP_ULP=espintcp from non-root + splice of setuid binary - pack2theroot — SUID bit set on /tmp/.suid_bash + dpkg invoked by packagekitd with /tmp/.pk-*.deb + 2x InstallFiles on same transaction Wiring: each module's .detect_yara and .detect_falco struct fields now point at the embedded string. The dispatcher dedups by pointer, so family-shared rules emit once across the 5 sub-modules. docs/DETECTION_PLAYBOOK.md augmented (302 -> 456 lines): - New 'YARA artifact scanning' subsection under SIEM integration with scheduled-scan cron pattern + per-rule trigger table - New 'Falco runtime detection' subsection with deploy + per-rule trigger table - New 'Per-module detection coverage' table — 4-format matrix - New 'Correlation across formats' section — multi-format incident signature per exploit (the 3-of-4 signal pattern) - New 'Worked example: catching DirtyDecrypt end-to-end' walkthrough from Falco page through yara confirmation, recovery, hunt + patch The existing operational lifecycle / SIEM patterns / FP tuning content is preserved unchanged — this commit only adds. Final stats: - auditd: 109 rule statements across 27 modules - sigma: 16 sigma rules across 19 modules - yara: 8 yara rules across 9 module headers (5 family + 4 distinct) - falco: 13 falco rules across 9 module headers The remaining 21 modules can gain YARA / Falco coverage incrementally by populating their detect_yara / detect_falco struct fields.
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@@ -660,6 +660,94 @@ static const char p2tr_auditd[] =
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"-a always,exit -F arch=b64 -S execve -F path=/usr/bin/apt-get \\\n"
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" -F auid!=0 -k skeletonkey-pack2theroot-apt\n";
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static const char p2tr_yara[] =
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"rule pack2theroot_malicious_deb : cve_2026_41651\n"
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"{\n"
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" meta:\n"
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" cve = \"CVE-2026-41651\"\n"
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" description = \"Pack2TheRoot payload .deb: small ar archive whose postinst installs a setuid copy of bash to /tmp/.suid_bash. The Vozec PoC + SKELETONKEY's port both leave this artifact in /tmp.\"\n"
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" author = \"SKELETONKEY\"\n"
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" reference = \"https://github.com/Vozec/CVE-2026-41651\"\n"
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" strings:\n"
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" $deb_magic = \"!<arch>\"\n"
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" $postinst_suid = \"install -m 4755 /bin/bash\"\n"
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" $skk_payload = \"Package: skeletonkey-p2tr-payload\"\n"
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" $skk_dummy = \"Package: skeletonkey-p2tr-dummy\"\n"
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" $vozec_payload = \"Package: pk-poc-payload\"\n"
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" $vozec_dummy = \"Package: pk-poc-dummy\"\n"
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" condition:\n"
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" // Small ar archive matching .deb layout, containing either\n"
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" // the published-PoC package names or the SUID-bash postinst.\n"
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" $deb_magic at 0 and\n"
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" ($postinst_suid or any of ($skk_payload, $skk_dummy, $vozec_payload, $vozec_dummy)) and\n"
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" filesize < 64KB\n"
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"}\n"
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"\n"
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"rule pack2theroot_suid_bash_drop : cve_2026_41651\n"
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"{\n"
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" meta:\n"
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" cve = \"CVE-2026-41651\"\n"
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" description = \"Pack2TheRoot SUID-bash artifact: /tmp/.suid_bash is the setuid bash dropped by the malicious postinst. Pair this YARA scan with auditd watch -w /tmp/.suid_bash for catch-on-create.\"\n"
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" author = \"SKELETONKEY\"\n"
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" strings:\n"
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" $elf = { 7F 45 4C 46 02 01 01 }\n"
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" $bash = \"GNU bash\"\n"
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" condition:\n"
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" // The rule itself can't see the file path; the operator\n"
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" // points YARA at /tmp/.suid_bash specifically. Match\n"
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" // confirms the file is a real bash ELF (not a planted decoy).\n"
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" $elf at 0 and $bash\n"
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"}\n";
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static const char p2tr_falco[] =
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"- rule: SUID bash dropped to /tmp (Pack2TheRoot postinst signature)\n"
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" desc: |\n"
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" A setuid bit appears on /tmp/.suid_bash. The Pack2TheRoot\n"
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" (CVE-2026-41651) malicious .deb postinst runs as root via\n"
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" the polkit-bypassed PackageKit transaction and lands a SUID\n"
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" copy of /bin/bash at this path.\n"
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" condition: >\n"
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" evt.type in (chmod, fchmod, fchmodat) and\n"
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" evt.arg.mode contains \"S_ISUID\" and\n"
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" fd.name = /tmp/.suid_bash\n"
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" output: >\n"
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" SUID bit set on /tmp/.suid_bash (proc=%proc.name pid=%proc.pid\n"
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" ppid=%proc.ppid parent=%proc.pname)\n"
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" priority: CRITICAL\n"
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" tags: [filesystem, mitre_privilege_escalation, T1068, cve.2026.41651]\n"
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"\n"
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"- rule: PackageKit InstallFiles invoked twice on same transaction (Pack2TheRoot TOCTOU)\n"
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" desc: |\n"
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" Two D-Bus InstallFiles() calls hit the same PackageKit\n"
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" transaction object in close succession — the exact shape of\n"
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" the Pack2TheRoot TOCTOU. Detection requires bus monitoring;\n"
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" Falco's k8s/audit ruleset doesn't cover D-Bus natively, but\n"
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" if dbus-monitor or systemd's bus audit is wired into the\n"
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" feed, this is the trigger.\n"
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" condition: >\n"
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" // Placeholder: requires dbus-monitor → falco feed.\n"
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" // Real-world deployment: pipe `dbus-monitor --system` into\n"
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" // a log-source rule keyed on the InstallFiles method name.\n"
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" proc.cmdline contains \"InstallFiles\" and proc.cmdline contains \"PackageKit\"\n"
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" output: >\n"
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" Possible Pack2TheRoot D-Bus TOCTOU shape (cmdline=\"%proc.cmdline\")\n"
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" priority: WARNING\n"
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" tags: [dbus, cve.2026.41651]\n"
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"\n"
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"- rule: dpkg invoked by PackageKit on behalf of non-root caller\n"
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" desc: |\n"
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" PackageKit forks dpkg to install a .deb on behalf of an\n"
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" unprivileged caller. Combined with /tmp/.suid_bash creation,\n"
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" this completes the Pack2TheRoot exploit chain.\n"
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" condition: >\n"
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" spawned_process and proc.name = dpkg and proc.aname = packagekitd and\n"
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" proc.cmdline contains \"/tmp/.pk-\"\n"
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" output: >\n"
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" PackageKit-driven dpkg install of /tmp-resident .deb\n"
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" (parent=%proc.pname cmdline=\"%proc.cmdline\")\n"
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" priority: CRITICAL\n"
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" tags: [process, cve.2026.41651, pack2theroot]\n";
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static const char p2tr_sigma[] =
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"title: Possible Pack2TheRoot exploitation (CVE-2026-41651)\n"
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"id: 3f2b8d54-skeletonkey-pack2theroot\n"
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@@ -700,8 +788,8 @@ const struct skeletonkey_module pack2theroot_module = {
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.cleanup = p2tr_cleanup,
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.detect_auditd = p2tr_auditd,
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.detect_sigma = p2tr_sigma,
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.detect_yara = NULL,
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.detect_falco = NULL,
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.detect_yara = p2tr_yara,
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.detect_falco = p2tr_falco,
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};
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void skeletonkey_register_pack2theroot(void)
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