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docs: record overlayfs_setuid (FUSE port needed) + sudoedit_editor findings
overlayfs_setuid (CVE-2023-0386) investigated on Ubuntu 22.04.0 / 5.15.0-25
(genuinely vulnerable): the non-FUSE chown copy-up yields upper/file owned by
uid 1000 (no escalation), and overlay refuses a userns-mounted FUSE lowerdir
with ENOSYS (plain overlay-in-userns works). A working exploit must mount FUSE
in the init ns via the setuid fusermount helper (fd-passing protocol) then
overlay in the userns — a substantial dedicated port. A raw /dev/fuse server
was written and reverted after hitting the ENOSYS wall.

sudoedit_editor (CVE-2023-22809) on sudo 1.9.9 returns EXPLOIT_FAIL — the
SUDO_EDITOR/-- arg injection reaches sudoedit's writable-dir guard; needs
target-file tuning and module debugging. Tractable next.

Ledger + VERIFICATIONS.jsonl updated. No code change (overlayfs_setuid reverted
to baseline; not committing a second non-working variant).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0118iUgHY44hdRtANgyCmu7y
2026-07-23 20:34:58 -04:00

6.6 KiB
Raw Blame History

Exploit verification ledger

What this is: results of actually running each exploit against a genuinely vulnerable VM and confirming uid=0 out of band (an independent root-owned write / /etc/shadow read / setuid-bash sentinel — never the module's own self-report). This is distinct from docs/VERIFICATIONS.jsonl's historical records, which only checked that detect() returns the right verdict.

Harness: rootless qemu/KVM over frozen point-release cloud images (unpatched → vulnerable by default), driver in the session scratch dir. Root witnessed via witness.sh (shell-probe + setuid-bash finisher + module sentinels + /etc/passwd tamper check).

Headline finding: the corpus was only ever detect-verified, never exploit-verified. Running the exploits shows a mix of genuinely-working, honestly-failing, and falsely-succeeding modules. Two flagship modules reported EXPLOIT_OK while obtaining no root at all (pwnkit, ptrace_traceme) — a false positive from the dispatcher's "execve transferred → clean child exit = OK" path. Both are addressed below.

Confirmed landing root (uid=0 witnessed out of band)

module CVE target notes
refluxfs CVE-2026-64600 Rocky 9.8 / 5.14.0-687.el9 full chain, /etc/passwd → root (earlier)
overlayfs CVE-2021-3493 Ubuntu 20.04.0 / 5.4.0-26 userns + xattr copy-up, clean
pwnkit CVE-2021-4034 Ubuntu 20.04.0 / polkit 0.105-26ubuntu1 after a fix — see below
sudo_runas_neg1 CVE-2019-14287 Ubuntu 18.04.2 / sudo 1.8.21p2 + sudoers (ALL,!root) sudo -u#-1 → uid 0

Fixed this session

  • pwnkit — reported EXPLOIT_OK but did not root (glibc "Could not open converter … to PWNKIT"). Root cause: missing the GCONV_PATH=. re-injection directory + chdir(workdir). Fixed → now lands real root on a vulnerable host. (commit 24b839e)
  • ptrace_traceme — reported EXPLOIT_OK but did not root; the bundled ptrace sequence is a non-working placeholder (it PTRACE_ATTACHes to the tracer, which by then has reparented to init → EPERM). Made honest (verifies euid==0, otherwise EXPLOIT_FAIL); a faithful CVE-2019-13272 port (Jann Horn / bcoles: PTRACE_TRACEME + setuid execve + registered polkit agent) is still required to land root. (commit 59cc2be)
  • cgroup_release_agent — two real bugs fixed (commit 8c45b2b): it read getuid() after unshare(CLONE_NEWUSER) (→ 65534, so uid_map write was "0 65534 1" → EPERM), and it omitted CLONE_NEWCGROUP (→ cgroup-v1 mount EPERM). Now the userns+cgroupns+mount setup is correct. It still can't root a bare unprivileged user on a stock systemd host: every v1 controller is pre-mounted (its release_agent is init-owned → EACCES from the userns) and a fresh named hierarchy is refused. Reachable in a container context (CAP_SYS_ADMIN / an ownable cgroup) — matches its "host root from rootless container" framing. The getuid()-after-unshare bug is a pattern to grep for across the other userns modules.

Needs a faithful PoC port (genuinely vulnerable target, exploit doesn't land)

module CVE target tested what's wrong
ptrace_traceme CVE-2019-13272 Ubuntu 18.04.2 / 4.15.0-50 placeholder technique (now honest); needs the real cred-transfer PoC (polkit agent) — substantial port
overlayfs_setuid CVE-2023-0386 Ubuntu 22.04.0 / 5.15.0-25 genuinely vulnerable target. Investigated deeply (this session): the non-FUSE chown copy-up produces upper/file owned by uid 1000, not root here, so it doesn't escalate — the CVE needs the FUSE-reported-uid-0 lower. But overlay refuses a userns-mounted FUSE lowerdir with ENOSYS (plain overlay-in-userns works; FUSE-lower does not). A working port must mount FUSE in the init ns via the setuid fusermount helper (implement its fd-passing unix-socket protocol, or link libfuse), then overlay in the userns. A raw /dev/fuse server was written and reverted (hit the overlay-on-userns-FUSE ENOSYS). Substantial dedicated port.
sudoedit_editor CVE-2023-22809 Ubuntu 22.04.0 / sudo 1.9.9 vulnerable sudo version + sudoers sudoedit grant present; module returns EXPLOIT_FAIL — the SUDO_EDITOR/-- arg-injection reaches sudoedit's writable-dir guard. Needs a target-file whose dir the injection can satisfy (e.g. /etc/passwd), and module debugging. Structural, tractable next.
sudo_samedit CVE-2021-3156 Ubuntu 18.04.2 + 20.04.0 honest EXPLOIT_FAIL; Baron Samedit is heap/libc-version-specific, needs a per-target tuned PoC. Hardest.

Inconclusive (detect version-blind vs vendor backport)

module CVE note
dirty_pipe CVE-2022-0847 Ubuntu 22.04.0's 5.15.0-25.25 almost certainly carries the backported fix (USN-5317); detect() is version-only so says VULNERABLE. Needs a genuinely pre-fix kernel (e.g. 5.13.0-19, or mainline 5.16.10) to verify the exploit.

Not yet exploit-tested (the bulk — ~30 modules)

  • 🟡 kernel primitives (nf_tables, nft_set_uaf, nft_payload, nft_fwd_dup, netfilter_xtcompat, af_packet, af_packet2, af_unix_gc, cls_route4, fuse_legacy, stackrot, sequoia, nft_pipapo, vsock_uaf, pintheft): return EXPLOIT_FAIL by design; landing root needs a per-kernel --dump-offsets + --full-chain (modprobe_path finisher) pass on a vulnerable kernel.
  • Structural userspace (sudoedit_editor, sudo_chwoot, sudo_host): need specific sudo versions + sudoers config; likely tractable.
  • 2026 CVEs (copy_fail ×5, dirtydecrypt, fragnesia, cifswitch, nft_catchall, ptrace_pidfd): need vulnerable 2026 kernels; the reconstructed race triggers (bad_epoll, ghostlock, nft_catchall) are deliberately under-driven and won't pop root by design.
  • Environment-blocked: vmwgfx (VMware guest only), dirty_cow (needs ≤4.4), mutagen_astronomy (CentOS 6 / Debian 7).
  • D-Bus/desktop (pack2theroot, udisks_libblockdev): need the polkit/D-Bus stack + a provisioner rule.

Method notes for continuation

  • Frozen images: cloud-images-archive.ubuntu.com/releases/<name>/release-<date>/ are unpatched and vulnerable-by-default for CVEs disclosed after that date — far easier than downgrading packages on current images.
  • gcc must be present in the VM (several exploits compile payloads at runtime); on EOL LTS, point apt at the archive main pocket.
  • Always verify root out of band. The module self-report is not trustworthy (two flagships lied). witness.sh is the reference check.