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.
This commit is contained in:
@@ -921,6 +921,55 @@ static const char dd_auditd[] =
|
||||
"-a always,exit -F arch=b64 -S splice -k skeletonkey-dirtydecrypt-splice\n"
|
||||
"-a always,exit -F arch=b32 -S splice -k skeletonkey-dirtydecrypt-splice\n";
|
||||
|
||||
static const char dd_yara[] =
|
||||
"rule dirtydecrypt_payload_overlay : cve_2026_31635 page_cache_write\n"
|
||||
"{\n"
|
||||
" meta:\n"
|
||||
" cve = \"CVE-2026-31635\"\n"
|
||||
" description = \"DirtyDecrypt payload: the 120-byte ET_DYN x86_64 ELF the public V12 PoC overlays onto the first bytes of a setuid binary's page cache. Scan setuid-root binaries (/usr/bin/su etc.); legitimate binaries are much larger and never start with this exact shellcode.\"\n"
|
||||
" author = \"SKELETONKEY\"\n"
|
||||
" reference = \"https://github.com/v12-security/pocs/tree/main/dirtydecrypt\"\n"
|
||||
" strings:\n"
|
||||
" // First 28 bytes of the embedded tiny_elf[] payload.\n"
|
||||
" $payload_head = { 7F 45 4C 46 02 01 01 00 00 00 00 00 00 00 00 00 03 00 3E 00 01 00 00 00 68 00 00 00 }\n"
|
||||
" // The setuid(0)+execve(/bin/sh) tail at offset 104 of the payload.\n"
|
||||
" $shellcode = { B0 69 0F 05 48 8D 3D DD FF FF FF 6A 3B 58 0F 05 }\n"
|
||||
" $sh = \"/bin/sh\"\n"
|
||||
" condition:\n"
|
||||
" // Setuid binaries are at minimum a few KB; the payload is\n"
|
||||
" // 120 bytes overlaid at offset 0 so the rest of the file\n"
|
||||
" // remains the original binary content (or padding).\n"
|
||||
" $payload_head at 0 and $shellcode and $sh and filesize > 4096\n"
|
||||
"}\n";
|
||||
|
||||
static const char dd_falco[] =
|
||||
"- rule: AF_RXRPC socket created by non-root (DirtyDecrypt primitive)\n"
|
||||
" desc: |\n"
|
||||
" Non-root process creates an AF_RXRPC socket. AF_RXRPC is the\n"
|
||||
" family the DirtyDecrypt (CVE-2026-31635) primitive needs to\n"
|
||||
" trigger the rxgk in-place decrypt. Most production hosts do\n"
|
||||
" not use AF_RXRPC at all (it's AFS-flavoured); a non-root\n"
|
||||
" open here is highly suspicious.\n"
|
||||
" condition: >\n"
|
||||
" evt.type = socket and evt.arg[0] = 33 and not user.uid = 0\n"
|
||||
" output: >\n"
|
||||
" AF_RXRPC socket() by non-root (user=%user.name proc=%proc.name\n"
|
||||
" pid=%proc.pid parent=%proc.pname)\n"
|
||||
" priority: CRITICAL\n"
|
||||
" tags: [process, mitre_privilege_escalation, T1068, cve.2026.31635]\n"
|
||||
"\n"
|
||||
"- rule: rxrpc security key added (DirtyDecrypt handshake setup)\n"
|
||||
" desc: |\n"
|
||||
" add_key(\"rxrpc\", …) by a non-root process — the DirtyDecrypt\n"
|
||||
" PoC adds an rxrpc-typed key carrying a forged rxgk XDR token\n"
|
||||
" for each fire() of the page-cache write primitive.\n"
|
||||
" condition: >\n"
|
||||
" evt.type = add_key and evt.arg[0] contains \"rxrpc\" and not user.uid = 0\n"
|
||||
" output: >\n"
|
||||
" rxrpc add_key by non-root (user=%user.name proc=%proc.name)\n"
|
||||
" priority: WARNING\n"
|
||||
" tags: [process, cve.2026.31635]\n";
|
||||
|
||||
static const char dd_sigma[] =
|
||||
"title: Possible DirtyDecrypt exploitation (CVE-2026-31635)\n"
|
||||
"id: 7c1e9a40-skeletonkey-dirtydecrypt\n"
|
||||
@@ -953,8 +1002,8 @@ const struct skeletonkey_module dirtydecrypt_module = {
|
||||
.cleanup = dd_cleanup,
|
||||
.detect_auditd = dd_auditd,
|
||||
.detect_sigma = dd_sigma,
|
||||
.detect_yara = NULL,
|
||||
.detect_falco = NULL,
|
||||
.detect_yara = dd_yara,
|
||||
.detect_falco = dd_falco,
|
||||
};
|
||||
|
||||
void skeletonkey_register_dirtydecrypt(void)
|
||||
|
||||
Reference in New Issue
Block a user