CVE-2026-80733
Received Received - Intake

Kernel Multicast Loopback Warning in Linux

Publication date: 2026-09-03

Last updated on: 2026-09-03

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: remove WARN_ON_ONCE() from sk_mc_loop() sk_mc_loop() can be called for sockets that are neither AF_INET nor AF_INET6 (e.g. AF_PACKET sockets when sending packets via raw/packet socket over virtual devices such as VRF or ipvlan). In such cases, sk_family is not AF_INET/AF_INET6 and sk_mc_loop() falls through the switch statement and triggers WARN_ON_ONCE(1). Non-INET sockets do not support IP_MULTICAST_LOOP or IPV6_MULTICAST_LOOP options, so loopback should default to true without generating a warning.

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Meta Information

Published
2026-09-03
Last Modified
2026-09-03
Generated
2026-09-03
AI Q&A
2026-09-03
EPSS Evaluated
N/A
NVD
CVE-2026-80733
EUVD
EUVD-2026-70337

Affected Vendors & Products

Currently, no data is known.

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a warning triggered by sk_mc_loop() when called on sockets not using AF_INET or AF_INET6, such as AF_PACKET sockets. The function incorrectly assumes only INET sockets are used, causing a WARN_ON_ONCE(1) error. Non-INET sockets do not support multicast loop options, so the warning is unnecessary.

Detection Guidance

This vulnerability is related to kernel warnings triggered by sk_mc_loop() when handling non-INET sockets. Detection involves checking kernel logs for WARN_ON_ONCE messages related to sk_mc_loop(). Use commands like dmesg | grep sk_mc_loop or journalctl -k | grep sk_mc_loop to search for these warnings in system logs.

Impact Analysis

This vulnerability may cause kernel warnings or logs when using non-INET sockets like AF_PACKET with virtual devices (e.g., VRF or ipvlan). It does not directly affect security but could lead to system logs being cluttered with warnings or potential performance overhead from repeated warnings.

Mitigation Strategies

Apply the latest Linux kernel update provided by your distribution to resolve the issue. If immediate patching is not possible, monitor kernel logs for related warnings and avoid using AF_PACKET sockets with virtual devices like VRF or ipvlan until patched.

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