Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
zephyrproject zephyr — Missing hop-limit decrement on IPv6 forwarding path allows unbounded packet looping (DoS) in Zephyr routers
AV AC PR UI S C I A CVSS EPSS %ile KEV
N L N N U N N H 7.5 .0029 22.0 —
AFFECTED
Product Versions Fixed
zephyr 1.8.0 – —
TIMELINE
Jun 2 Reserved by zephyr
Jul 31 EXPLOIT PUBLISHED — CVE-2026-10686 (zephyrproject zephyr). Public exploit reference added.
Jul 31 Published (CNA: zephyr)
Description
Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. Both routing branches of ipv6_route_packet() (subsys/net/ip) were affected: the explicit-route path (net_route_packet()) and the on-link cross-interface path (net_route_packet_if()). Each set the packet forwarding flag and called net_send_data() 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 CONFIG_NET_ROUTE (enabled by default when CONFIG_NET_IPV6_NBR_CACHE is set), together with CONFIG_NET_ROUTING for cross-interface routing. Note that CONFIG_NET_IPV6_FORWARDING and CONFIG_NET_IPV4_FORWARDING — 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 CONFIG_NET_ROUTE and CONFIG_NET_ROUTING.
IPv4 is not affected in any release. The IPv4 forwarding path (net_route_ipv4_packet() in route_ipv4.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 net_route_packet() and v2.2.0 added net_route_packet_if(), 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).
Lifecycle
Complete event history — 3 events, chronological
| Date | Event | Detail |
|---|
| June 2, 2026 | Reserved | Reserved by zephyr |
| July 31, 2026 | EXPLOIT PUBLISHED | EXPLOIT PUBLISHED — CVE-2026-10686 (zephyrproject zephyr). Public exploit reference added. |
| July 31, 2026 | Published | Published (CNA: zephyr) |
Affected
Affected products and packages — 1 row
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|
| zephyrproject | zephyr | — | 1.8.0 | — |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-10686 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.