{"affected":[{"defaultStatus":"unaffected","ecosystem":"https://github.com/zephyrproject-rtos/zephyr","packageName":"zephyr","product":"zephyr","source":"CNA: zephyr","vendor":"zephyrproject","versions":[{"lessThan":"4.3.2","status":"affected","version":"1.8.0","versionType":"semver"},{"lessThan":"4.4.2","status":"affected","version":"4.4.0","versionType":"semver"}]}],"cveId":"CVE-2026-12633","cwes":["CWE-787"],"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.\n\nWith 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.\n\nThe 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.\n\nThe 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.","epss":{"date":"2026-11-03","percentile":0.24166,"score":0.00312},"exploits":[],"kev":null,"metrics":[{"score":8.1,"severity":"high","source":"CNA: zephyr","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","version":"3.1"},{"score":8.1,"severity":"high","source":"NVD: vulnerabilities@zephyrproject.org","vector":"CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","version":"3.1"}],"modifiedAt":1793769520707,"publishedAt":1787171854532,"references":[{"source":"CNA: zephyr","tags":["patch"],"url":"https://github.com/zephyrproject-rtos/zephyr/commit/15e838c739be637bf23fd56a5c26f2b32079551b"},{"source":"CNA: zephyr","tags":[],"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-h5m5-hm6j-cgpf"},{"source":"vulnerabilities@zephyrproject.org","tags":[],"url":"https://github.com/zephyrproject-rtos/zephyr/commit/15e838c739be637bf23fd56a5c26f2b32079551b"},{"source":"vulnerabilities@zephyrproject.org","tags":[],"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-h5m5-hm6j-cgpf"}],"remediation":[{"kind":"fix","source":"CNA: zephyr","text":"The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.","url":"https://github.com/zephyrproject-rtos/zephyr/commit/15e838c739be637bf23fd56a5c26f2b32079551b"}],"revision":"deecad17df04beffb9bfa39e815f3cbf02d2069ca2f50f3648579cc2c936756c","sources":[{"modifiedAt":1793768373616,"name":"CNA: zephyr","retrievedAt":1793769028126,"url":"https://www.cve.org/CVERecord?id=CVE-2026-12633"},{"modifiedAt":1793769520707,"name":"NVD","retrievedAt":1793772957556,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-12633"},{"modifiedAt":null,"name":"FIRST EPSS","retrievedAt":1793769048611,"url":"https://api.first.org/data/v1/epss?cve=CVE-2026-12633"}],"ssvc":{"assessedAt":1787238975491,"automatable":"no","exploitation":"none","source":"ADP: CISA-ADP","technicalImpact":"partial"},"status":"published","title":"Out-of-bounds write in IPv6 6LoWPAN Context Option handling via unauthenticated Router Advertisement","updatedAt":1793772957556}