CVE-2021-47293: net/sched: act_skbmod: Skip non-Ethernet packets

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-21 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_skbmod: Skip non-Ethernet packets Currently tcf_skbmod_act() assumes that packets use Ethernet as their L2 protocol, which is not always the case. As an example, for CAN devices: $ ip link add dev vcan0 type vcan $ ip link set up vcan0 $ tc qdisc add dev vcan0 root handle 1: htb $ tc filter add dev vcan0 parent 1: protocol ip prio 10 \ matchall action skbmod swap mac Doing the above silently corrupts all the packets. Do not perform skbmod actions for non-Ethernet packets.

Affected products

Linux kernel: from 4.9 before 4.19.199; from 4.20 before 5.4.136; from 5.5 before 5.10.54; from 5.11 before 5.13.6; 5.14-rc1, 5.14-rc2 — fixed in 4.19.199, 5.10.54, 5.13.6, 5.4.136

How to fix

Upgrade to a fixed version: Linux kernel 4.19.199, 5.10.54, 5.13.6, 5.4.136. Check the vendor advisory for mitigations.

References

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