modules: add ptrace_pidfd (CVE-2026-46333, Qualys ptrace/pidfd_getfd cred-steal)

New module for Qualys's 2026-05-20 disclosure: a __ptrace_may_access logic flaw leaves a process dropping privileges briefly reachable past its dumpable boundary; pidfd_getfd(2) steals root-opened fds / authenticated channels from it. Default-distro, no userns, arch-agnostic (fd-steal, no shellcode).

detect(): version-pinned, predates-gate at pidfd_getfd's 5.6 introduction; kernel_range from Debian backports (5.10.251/6.1.172/6.12.88/7.0.7), drift-check clean. exploit(): spawns a setuid victim, pidfd_open()s it, sweeps pidfd_getfd() over its fd table during the cred-drop window, reports any uid-0-owned fd captured from a non-root context. Honest EXPLOIT_FAIL without a euid-0 witness; not yet VM-verified. mitigate(): yama ptrace_scope=2; cleanup() reverts. auditd/sigma/falco rules, NOTICE.md (Qualys TRU credit) + MODULE.md, safety rank 84.

Wiring: registry, Makefile, cve_metadata (+JSON source), verify-vm/targets.yaml (ubuntu2204 + mainline 5.15.5 target, sweep pending). Docs: README + CVES.md + docs/index.html counts 39->40 modules / 34->35 CVEs; added to not-yet-verified lists + corpus pill.

skeletonkey.c

@@ -1014,6 +1014,7 @@ static int module_safety_rank(const char *n)
     if (!strcmp(n, "dirtydecrypt") ||
         !strcmp(n, "fragnesia"))             return 87;  /* ported page-cache writes; version-pinned detect, exploit NOT VM-verified */
     if (!strcmp(n, "ptrace_traceme"))        return 85;  /* userspace cred race */
+    if (!strcmp(n, "ptrace_pidfd"))          return 84;  /* pidfd_getfd fd-steal race; ported, exploit NOT VM-verified */
     if (!strcmp(n, "sudo_samedit"))          return 80;  /* heap-tuned, may crash sudo */
     if (!strcmp(n, "af_unix_gc"))            return 25;  /* kernel race, low win% */
     if (!strcmp(n, "stackrot"))              return 15;  /* very low win% */