Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. Both routing branches of ipv6routepacket() (subsys/net/ip) were affected: the explicit-route path (netroutepacket()) and the on-link cross-interface path (netroutepacketif()). Each set the packet forwarding flag and called netsenddata() with the hop limit untouched and no expiry check.
Per RFC 8200 the hop-limit decrement is the mechanism that bounds packet lifetime and terminates routing loops; without it, a device acting as an IPv6 router relays looping packets indefinitely. An on-path attacker who can induce or exploit a transient L3 loop turns it into a permanent forwarding storm, causing CPU/bandwidth resource exhaustion (availability DoS) on the forwarder and adjacent links; path-discovery and loop diagnostics that rely on hop-limit expiry are also defeated.
Affected configurations. In every affected release the forwarding path is reached via CONFIGNETROUTE (enabled by default when CONFIGNETIPV6NBRCACHE is set), together with CONFIGNETROUTING for cross-interface routing. Note that CONFIGNETIPV6FORWARDING and CONFIGNETIPV4FORWARDING — which appear in the fix and in this advisory's evidence notes — were introduced after v4.4.0, when the routing options were split and renamed; they do not exist in any affected release. When auditing a v4.4.1-or-earlier configuration, look for CONFIGNETROUTE and CONFIGNETROUTING.
IPv4 is not affected in any release. The IPv4 forwarding path (netrouteipv4packet() in routeipv4.c) was added after v4.4.0 and has never shipped in a release. Its TTL decrement and IPv4 header-checksum recomputation landed on main as part of the same fix, so the evidence notes below discuss it, but no released version is reachable by way of IPv4.
Affected releases are v1.8.0 through v4.4.1: v1.8.0 introduced netroutepacket() and v2.2.0 added netroutepacketif(), and neither decremented the hop limit. v4.3.1 carries the explicit-route fix but not the on-link one, so it is affected as well. Fixed on main by 7d8f1afa7345 (explicit-route path) and 589eadc74efa (on-link path).
The DesignWare SPI driver (drivers/spi/spidw.c) computed the SPI BAUDR clock divider as info->clockfrequency / config->frequency without validating config->frequency.
spitransceive is a Zephyr syscall and its verify handler (drivers/spi/spihandlers.c) copies the caller-supplied spiconfig from userspace without checking the frequency field, so a userspace thread that has been granted access to a DesignWare SPI device kernel object can pass frequency = 0 and trigger an unsigned integer divide-by-zero in spidwconfigure().
On Cortex-M Mainline (SCB->CCR.DIV0TRP is set in zarmfaultinit()) and on ARC (a dedicated evdivzero vector) this raises a CPU exception, resulting in a kernel fault and local denial of service.
The fix rejects zero frequency and frequencies above clockfrequency / 2 (the DesignWare SSI databook minimum SCKDIV of 2) with -EINVAL. The defect affects all Zephyr releases up to and including v4.4.0; exploitation requires CONFIGUSERSPACE=y and an unprivileged thread already granted SPI driver permission. There is no memory-corruption or information-disclosure impact.