device_digest is not unique across boards, weakening the USB provisioning anti-swap guard

[proffesor-for-testing]

device_digest is not unique across boards, weakening the USB provisioning anti-swap guard

Repo: ruvnet/RuView (firmware) · Severity: Medium-High · Measured: 2026-09-14, three ESP32-C6 boards on 0.8.12

Symptom

Two physically distinct boards report the same device_digest over RUVIEW_HELLO_V1:

node 11   device_digest=062009cef304369d
node 12   device_digest=062009cef304369d    <-- identical
node 13   device_digest=e1303fbd5cd4cebd

Read in one pass across three ports, each nonce-matched, stable across reboots and across a
firmware reflash. Confirmed distinct hardware — esptool reports different efuse base MACs
for all three.

Not duplicate efuses

The firmware computes SHA-256("ruview-device-v1" || esp_efuse_mac_get_default())[0..8].
With distinct base MACs the digests cannot collide, so this was checked directly. Brute
force over the documented formula and every plausible variant — domain with and without the
NUL, raw / reversed / lowercase-hex / uppercase-hex / colon-separated MAC, 6-byte base and
8-byte extended MAC, prefix and suffix ordering — reproduces none of the three observed
digests, including the unique one.

So the shipped digest is not a function of the MAC in the way the source describes, and it
is not the all-zeros failure path either: the firmware believes it succeeded. It is silently
wrong rather than failing closed.

Impact

deviceDigest is the anti-swap guard in Mac USB provisioning
(RuViewNodeOnboardingModule.swift:119):

let attempt = try hello(on: descriptor, path: portPath, ...)
guard let hello = attempt.node, hello.deviceDigest == expectedDeviceDigest else {
  throw RuViewNodeOnboardingError.identityMismatch
}

It re-runs HELLO before writing NVS to confirm the board is the one the operator selected.
With a colliding digest that guard cannot distinguish those two boards, so it degrades from
"verified identity" to "verified chip family". Serial paths do re-enumerate in practice —
observed during flashing — so a mix-up is reachable, and would write the wrong node ID to
the wrong board.

Detection is unaffected: the device list keys on serial path, so all boards appear
correctly.

Caveat on attribution

release_bins/c6-onboarding/esp32-csi-node.bin is a tracked binary blob, so it cannot be
proven that the serial_onboarding.c in the tree is the source that built it. The behaviour
is measured and reproducible; the cause needs a from-source rebuild to pin down.