CVE-2026-16515 (GCVE-0-2026-16515)

Vulnerability from cvelistv5 – Published: 2026-09-18 14:30 – Updated: 2026-11-04 05:00
VLAI
Title
ICMPv6 error messages sent for multicast-destined packets and non-unique source addresses enable network amplification in Zephyr's IPv6 stack
Summary
net_icmpv6_send_error() in subsys/net/ip/icmpv6.c implemented only one of the three RFC 4443 section 2.4 suppression rules (do not answer an ICMPv6 error with an ICMPv6 error). It did not check whether the triggering packet's source address identifies a single node (rule e.6) or whether the packet was sent to a multicast destination (rule e.3, whose only exceptions are Packet Too Big and Parameter Problem Code 2). Of the five call sites, only the port-unreachable path in subsys/net/ip/connection.c carried an equivalent guard of its own; the extension-header, unknown-next-header and fragmentation paths in subsys/net/ip/ipv6.c and subsys/net/ip/ipv6_fragment.c had none. An unauthenticated attacker with access to the same link can exploit this in two ways. Sending a single IPv6 packet to the link-local all-nodes group ff02::1 carrying an unrecognized next-header value, with the source address spoofed to a chosen victim, causes every Zephyr node on the link to emit an ICMPv6 Parameter Problem message to that victim — a reflector with an amplification factor equal to the number of nodes. Alternatively, sending a unicast packet whose source address is a multicast address causes the node to transmit its ICMPv6 error to that multicast address, turning one unicast packet into a link-flooded multicast frame. Packets addressed to ff02::1 are accepted unconditionally by ipv6_input(), and no check rejects a multicast source address, so no special configuration is required. The impact is degraded availability of the shared link and of the reflection victim, together with the ability for the attacker to hide its own address behind the responding nodes. The effect is amplified on constrained mesh links such as 802.15.4/Thread, where link-local multicast is flooded hop by hop. There is no memory-safety consequence: the error packet itself is well formed, it is simply emitted in cases where the protocol forbids it. The fix adds both suppression checks at the single choke point in net_icmpv6_send_error(), before any reply packet is allocated, preserving the RFC-mandated exceptions for NET_ICMPV6_PACKET_TOO_BIG and Parameter Problem Code 2. Note that the IPv4 counterpart net_icmpv4_send_error() in subsys/net/ip/icmpv4.c still checks only for a broadcast destination and retains an equivalent gap for multicast destinations and non-unique sources.
Severity
4.7 (Medium)
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-18 16:25 UTC
CWE
Assigner
zephyr CNA under the mitre root
CNA scorecard B 77/100 over 238 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
zephyrproject zephyr Affected: 1.14.0 , < 4.3.2 (semver)
Affected: 4.4.0 , < 4.4.2 (semver)
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

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