CVE-2026-12633 (GCVE-0-2026-12633)
Vulnerability from cvelistv5 – Published: 2026-08-19 20:37 – Updated: 2026-11-04 04:59
VLAI
EPSS
VEX
Title
Out-of-bounds write in IPv6 6LoWPAN Context Option handling via unauthenticated Router Advertisement
Summary
The IPv6 neighbor-discovery code in subsys/net/ip/ipv6_nbr.c processes the 6LoWPAN Context Option (6CO, RFC 6775) carried inside ICMPv6 Router Advertisements. In handle_ra_6co() the 8-bit context_len field is taken directly from the packet and was never bounded to the RFC maximum of 128. The function computes context->context_len / 8 and then performs memset(context->prefix + context_len, 0, sizeof(context->prefix) - context_len), where context->prefix is a fixed 16-byte array.
With context_len between 136 and 255 (and the option length field set to 3, which the pre-fix validation accepts), context_len / 8 evaluates to 17..31, so the memset length 16 - context_len/8 underflows the unsigned size_t argument to roughly SIZE_MAX. This produces an unbounded out-of-bounds memset that zeroes kernel memory well past the 6lo context structure.
The defect is reachable from unauthenticated, link-local input: any host on the same link can send a crafted Router Advertisement with a 6CO option. The RA handler validates only the option length field before calling handle_ra_6co(), so a single packet triggers the wild write. The code is compiled when CONFIG_NET_6LO_CONTEXT is enabled.
The impact is a reliable remote (adjacent) denial of service via memory corruption, with collateral integrity loss as the memset zeroes contiguous memory before the system faults. Router Advertisements are link-scoped and not forwarded, so the attacker must be on the same link (AV:A). The fix rejects any context_len greater than 128 before the length computation.
Severity
8.1 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-20 15:16 UTC
CWE
- CWE-787 - memory-safety
Assigner
zephyr
CNA
References
2 references
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| zephyrproject | zephyr |
Affected:
1.8.0 , < 4.3.2
(semver)
Affected: 4.4.0 , < 4.4.2 (semver) |
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