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CVE-2026-12633

HIGHCVSS 8.1/10EPSS 0.21%

Last modified

CVE-2026-12633 is a high-severity vulnerability rated 8.1/10 on the CVSS scale. 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. EPSS estimates a 0.21% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1
8.1/10

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

EPSS Probability
0.21%

11.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
zephyrprojectzephyr>= 1.8.0, < 4.4.2

References

Timeline

Published
Last Modified
Status
Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-12633?
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.
How severe is CVE-2026-12633?
CVE-2026-12633 has a CVSS score of 8.1/10 (HIGH severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.
How do I fix CVE-2026-12633?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST