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.

modules/ptrace_pidfd_cve_2026_46333/NOTICE.md

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+# NOTICE — ptrace_pidfd (CVE-2026-46333)
+
+## Vulnerability
+
+**CVE-2026-46333** — a logic flaw in the Linux kernel's
+`__ptrace_may_access()` path leaves a privileged process that is
+*dropping* its credentials briefly reachable through ptrace-family
+operations, even though its `dumpable` flag should already have closed
+that path. Paired with `pidfd_getfd(2)`, an unprivileged local user can
+capture open file descriptors and authenticated IPC channels from a
+dying privileged process and re-use them under their own uid → local
+root and credential disclosure.
+
+The underlying flaw has resided in mainline since **v4.10-rc1**
+(November 2016); the `pidfd_getfd(2)` exploitation vector was added in
+**v5.6** (January 2020). Affects default installations of Debian 13,
+Ubuntu 24.04 / 26.04, Fedora 43 / 44, SUSE, AlmaLinux, and CloudLinux.
+
+## Research credit
+
+Discovered and disclosed by **Qualys Threat Research Unit (TRU)**,
+published 2026-05-20. The four proof-of-concept exploits demonstrated
+by Qualys targeted `chage`, `ssh-keysign`, `pkexec`, and
+`accounts-daemon`.
+
+- Qualys advisory:
+  <https://blog.qualys.com/vulnerabilities-threat-research/2026/05/20/cve-2026-46333-local-root-privilege-escalation-and-credential-disclosure-in-the-linux-kernel-ptrace-path>
+- Upstream fix: mainline, committed 2026-05-14.
+- Debian-tracked stable backports: 5.10.251 (bullseye) / 6.1.172
+  (bookworm) / 6.12.88 (trixie) / 7.0.7 (forky, sid).
+
+All research credit for finding and analysing this bug belongs to
+Qualys. SKELETONKEY is the bundling and bookkeeping layer only.
+
+## SKELETONKEY role
+
+🟡 **Primitive / ported-from-disclosure — not yet VM-verified.**
+`detect()` is version-pinned against the Debian backport thresholds
+above (kernels < 5.6 are reported OK, lacking the bundled vector).
+`exploit()` fires the real primitive: it spawns a setuid victim,
+`pidfd_open()`s it, and sweeps `pidfd_getfd()` across its descriptor
+table during the credential-drop window, recording whether a root-owned
+descriptor is actually captured from a non-root context. It returns
+`EXPLOIT_FAIL` unless it can witness euid 0 — the target-specific
+fd-weaponization that lands a root shell is **not** bundled until it can
+be verified end-to-end against a real vulnerable VM, in keeping with the
+project's no-fabrication rule.
+
+`--mitigate` sets `kernel.yama.ptrace_scope=2` (the check `pidfd_getfd`
+rides); `--cleanup` restores it. Architecture-agnostic — the technique
+steals descriptors rather than injecting shellcode.