modules: add cifswitch (CVE-2026-46243, Asim Manizada's CIFSwitch)

CIFSwitch is the newest kernel-7-era LPE not already in the corpus: a
~19-year-old logic flaw in fs/smb/client/cifs_spnego.c where the
cifs.spnego request-key type accepts key descriptions created by
userspace (add_key(2)/request_key(2)) without verifying the request came
from the in-kernel CIFS client. The description's authority-bearing
fields (pid/uid/creduid/upcall_target) are trusted by the root cifs.upcall
helper; with user+mount namespace tricks an unprivileged user coerces
cifs.upcall into loading an attacker NSS module as root. Fixed upstream by
3da1fdf4efbc (merged 7.1-rc5); CWE-20; not in CISA KEV.

Takes the corpus to 42 modules / 37 CVEs.

🟡 honest port — full chain not VM-verified. detect() gates on the kernel
version (Debian backports 5.10.257/6.1.174/6.12.90/7.0.10) AND on the
cifs userspace path (cifs.upcall / cifs.spnego request-key rule), so a
vulnerable kernel without cifs-utils is PRECOND_FAIL not a false positive
(override via SKELETONKEY_CIFS_ASSUME_PRESENT=1/0). exploit() fires only
the non-destructive add_key(2) cifs.spnego probe (no upcall, loads
nothing, revoked immediately) and returns EXPLOIT_FAIL without a euid-0
witness — the namespace+NSS root-pop is not bundled until VM-verified.
--mitigate blocklists the cifs module; --cleanup reverts.

Wired everywhere: registry, Makefile, safety rank (86), 6 detect() test
rows (env-driven precondition override), CVE_METADATA.json + cve_metadata.c
+ KEV_CROSSREF.md (sorted insert, CWE-20/T1068/not-KEV), README + CVES.md
+ website counts (42/37) and a yellow module pill, RELEASE_NOTES v0.9.10,
verify-vm target (sweep pending). Credit: Asim Manizada. Version 0.9.10.

docs/RELEASE_NOTES.md

@@ -1,3 +1,38 @@
+## SKELETONKEY v0.9.10 — new LPE module: cifswitch (CVE-2026-46243)
+
+Adds **`cifswitch` — CVE-2026-46243 "CIFSwitch"** (Asim Manizada,
+2026-05-28), taking the corpus to **42 modules / 37 CVEs**. The newest
+kernel-7-era LPE not already covered: a ~19-year-old logic flaw in
+`fs/smb/client/cifs_spnego.c` where the `cifs.spnego` request-key type
+accepts key descriptions created by *userspace* (`add_key(2)` /
+`request_key(2)`) without verifying the request came from the in-kernel
+CIFS client. The description carries authority-bearing fields
+(`pid`/`uid`/`creduid`/`upcall_target`) that the root `cifs.upcall`
+helper trusts as kernel-originating; combined with user+mount namespace
+tricks, an unprivileged user coerces `cifs.upcall` into loading an
+attacker NSS module as root. Fixed upstream by `3da1fdf4efbc` (merged
+7.1-rc5); NVD class CWE-20; not in CISA KEV.
+
+🟡 **Honest port — full chain not VM-verified.** `detect()` gates on the
+kernel version (Debian backports 5.10.257 / 6.1.174 / 6.12.90 / 7.0.10)
+**and** on the presence of the vulnerable userspace path — a vulnerable
+kernel without `cifs-utils` reports `PRECOND_FAIL`, not a false
+`VULNERABLE` (override the probe with `SKELETONKEY_CIFS_ASSUME_PRESENT=1`
+/`0`). `exploit()` fires only the non-destructive primitive — `add_key(2)`
+of a forged-but-benign `cifs.spnego` key, which does **not** invoke
+`cifs.upcall` and loads nothing, revoked immediately — and treats a clean
+accept as the empirical witness that userspace can forge the
+authority-bearing key type. It then stops: the namespace-switch +
+malicious-NSS-load root-pop is target/config-specific and is not bundled
+until VM-verified, so it returns honest `EXPLOIT_FAIL` without a euid-0
+witness (never fabricates root). `--mitigate` blocklists the `cifs`
+module (`/etc/modprobe.d/skeletonkey-disable-cifs.conf`); `--cleanup`
+reverts. Structural, arch-agnostic (keyring + namespace logic, no
+shellcode). Ships auditd + sigma + falco rules, MITRE ATT&CK T1068 +
+CWE-20 metadata, six new `detect()` unit-test rows, and credits Asim
+Manizada in `NOTICE.md`. Not yet VM-verified (sweep pending in
+`tools/verify-vm/targets.yaml`), so the verified count stays 28 of 37.
+
 ## SKELETONKEY v0.9.9 — install.sh needs no root; CVE-2022-0492 KEV drift
 
 Two maintenance fixes, no new modules.