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.
2026-06-02 08:26:24 -04:00
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+# ptrace_pidfd — CVE-2026-46333
+
+`__ptrace_may_access()` dumpable-race credential-descriptor theft via
+`pidfd_getfd(2)`.
+
+## The bug
+
+When a privileged process drops its credentials, the kernel resets its
+`dumpable` flag so that lower-privileged processes can no longer attach
+to it. CVE-2026-46333 is a logic flaw in `__ptrace_may_access()`: there
+is a narrow window during the credential drop in which the process is
+*still reachable* through ptrace-family access checks even though its
+`dumpable` state should already have closed that path.
+
+`pidfd_getfd(2)` performs a `PTRACE_MODE_ATTACH_REALCREDS` access check
+before duplicating a descriptor out of the target process. During the
+stale window that check wrongly succeeds, so an unprivileged process can
+pull descriptors — a root-opened credential file, or an authenticated
+D-Bus / socket channel — out of a transiently-privileged process and
+re-use them under its own uid.
+
+## Affected range
+
+| | |
+|---|---|
+| Flaw introduced | v4.10-rc1 (Nov 2016) in `__ptrace_may_access` |
+| Exploit vector added | `pidfd_getfd(2)` in v5.6 (Jan 2020) |
+| Fixed upstream | mainline, 2026-05-14 |
+| Debian backports | 5.10.251 · 6.1.172 · 6.12.88 · 7.0.7 |
+
+Branches Debian does not ship (5.15 / 6.6 / 6.18 / 6.19) are reported on
+the version-only verdict; run `--exploit ptrace_pidfd --i-know` to fire
+the real primitive and confirm empirically.
+
+## Trigger / detection
+
+`detect()` consults the shared host fingerprint, returns `OK` below 5.6
+(no vector) or for patched branches, otherwise `VULNERABLE`. No active
+probe — the empirical confirmation lives in the exploit path, which
+spawns a setuid victim and sweeps `pidfd_getfd()` over its descriptor
+table, reporting any uid-0-owned descriptor captured from a non-root
+context.
+
+## Fix / mitigation
+
+Upgrade the kernel. As a runtime stopgap, `kernel.yama.ptrace_scope=2`
+(or `3`) closes the `pidfd_getfd` path because it gates the same
+`__ptrace_may_access(ATTACH)` check; `--mitigate` applies it and
+`--cleanup` reverts it.
+
+## Credit
+
+Qualys Threat Research Unit (2026-05-20). See `NOTICE.md`.