GHSA-6j2r-xrm4-3v7f: OpenThread joiner autostart uses a publicly documented default Joining Device Credential (PSKd)
Zephyr's OpenThread integration defined CONFIGOPENTHREADJOINERPSKD with default "J01NME" in modules/openthread/Kconfig.thread (previously subsys/net/l2/openthread/Kconfig, then subsys/net/l2/openthread/Kconfig.thread). J01NME is the example Joining Device Credential used throughout the public OpenThread and Thread commissioning documentation, including Zephyr's own samples/net/sockets/echoclient/README.rst, so it is not a secret. A firmware image built with CONFIGOPENTHREADJOINERAUTOSTART=y that never overrode the PSKd therefore shipped with a publicly known joining credential compiled in, with no build-time or run-time warning.
The PSKd is the only value that authenticates Thread commissioning: joiner and commissioner run a DTLS-PSK handshake keyed on it, after which the commissioner supplies the full operational dataset. In otconfigureinstance() (modules/openthread/openthread.c), a device with no stored dataset calls otJoinerStart() with the configured PSKd, and otjoinerstarthandler() calls otThreadSetEnabled() on success. An unauthenticated attacker within 802.15.4 radio range of an uncommissioned device (factory-fresh, after a factory reset, or after a settings erase) can run any stock Thread commissioner registered with J01NME, complete the handshake, and hand the device an attacker-controlled operational dataset.
The device then joins and enables Thread on the attacker's mesh. The attacker becomes its router, seeing, dropping, injecting and spoofing all of the device's IPv6 traffic and impersonating the peers the application expects, while the device is cut off from the network it was meant to join and stays mis-provisioned until it is reset. Only application-layer security with independently provisioned credentials survives. Exposure is limited to builds that enable joiner autostart and leave the PSKd unset; the option is not enabled by default and no in-tree sample uses the vulnerable combination.
The fix removes the default from CONFIGOPENTHREADJOINERPSKD and adds a BUILDASSERT() in modules/openthread/openthread.c, active only under CONFIGOPENTHREADJOINERAUTOSTART, that fails the build unless a 6-to-32-character PSKd is configured. Products should provision a per-device PSKd from factory data and call otJoinerStart() from the application rather than relying on a credential compiled identically into every unit.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Provision a unique per-device PSKd from factory data instead of using the publicly documented default "J01NME"; preferably call otJoinerStart() from the application rather than relying on a credential compiled identically into every unit.
Zephyr OpenThread joiner autostart CONFIG_OPENTHREAD_JOINER_PSKD = A unique per-device PSKd with 6-32 characters
Event History
Frequently Asked Questions
Which devices are exposed in practice?
Devices are exposed when they are uncommissioned, including factory-fresh devices, devices after a factory reset, or devices whose settings have been erased. They must have been built with CONFIG_OPENTHREAD_JOINER_AUTOSTART=y and without overriding CONFIG_OPENTHREAD_JOINER_PSKD.
What does an attacker need to exploit this?
An attacker does not need prior authentication, but must be within 802.15.4 radio range of the uncommissioned device. The publicly documented PSKd can authenticate the Thread commissioning DTLS-PSK handshake, after which a commissioner supplies the operational dataset.
Are devices using the default configuration affected?
The vulnerable condition requires joiner autostart to be enabled and the PSKd to remain at its default value, J01NME. A build using a different configured PSKd is not affected by the documented default-credential condition.
How can an operator identify affected firmware or devices?
Review the firmware configuration for CONFIG_OPENTHREAD_JOINER_AUTOSTART=y and determine whether CONFIG_OPENTHREAD_JOINER_PSKD was overridden from J01NME. Devices meeting those conditions are at risk while they have no stored Thread operational dataset.