CVE-2026-12633

Adjacent denial of service via 6CO memset underflow

Published Aug 19, 2026 · Updated Aug 20, 2026

Out-of-bounds write in Zephyr Project Zephyr RTOS before 4.4.2 allows attackers to crash the kernel via a crafted Router Advertisement. In subsys/net/ip/ipv6_nbr.c, handle_ra_6co() accepts an unbounded 8-bit 6CO context_len, divides it by eight, and feeds the result into memset() for a fixed 16-byte prefix buffer; values above 128 make the remaining-length calculation underflow and zero memory past the 6LoWPAN context structure. Reachability requires CONFIG_NET_6LO_CONTEXT and network adjacency because Router Advertisements are link-scoped, so any host on the same link can trigger a reliable crash and unintended kernel-memory overwrites with one packet.

CVSS severity8.1
High
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in Zephyr Project Zephyr RTOS before 4.4.2 allows attackers to crash the kernel via a crafted Router Advertisement. In subsys/net/ip/ipv6_nbr.c, handle_ra_6co() accepts an unbounded 8-bit 6CO context_len, divides it by eight, and feeds the result into memset() for a fixed 16-byte prefix buffer; values above 128 make the remaining-length calculation underflow and zero memory past the 6LoWPAN context structure. Reachability requires CONFIG_NET_6LO_CONTEXT and network adjacency because Router Advertisements are link-scoped, so any host on the same link can trigger a reliable crash and unintended kernel-memory overwrites with one packet.

The record

CVE
CVE-2026-12633
Published
Aug 19, 2026
Updated
Aug 20, 2026
Vendor
Zephyr Project
Product
Zephyr RTOS
Classifications
CWE-787, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.8.0 <4.4.2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zephyr Project · Zephyr RTOSversion=1.8.0 <4.4.2

Published CVSS scores

8.1Zephyr ProjectCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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