CVE-2026-63868

What the bug is

The receive-side GARP attribute parser computes dlen with reversed operands: dlen = sizeof(*ga) - ga->len; ga->len is the on-wire attribute length and includes the GARP attribute header. For normal attributes with data, ga->len is larger than sizeof(*ga), so the subtraction underflows in unsigned arithmetic. The resulting value is later passed to garp_attr_lookup(), whose length argument is u8. After truncation, the parsed data length usually no longer matches the length stored for locally registered attributes, so received Join/Leave events are ignored. This breaks the GARP receive path for common attributes, such as GVRP VLAN registration attributes. Compute the data length as the attribute length minus the header length.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

net/802/garp.c

What this is

NETWORKING [GENERAL]MAINTAINERS section matched on net/ · netdev@vger.kernel.org · Maintained

Kernel module

garp

Check it on the machine

grep -w CONFIG_GARP /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

lsmod | grep -w garp

Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.

Show whether Debian builds this, per release

Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.

• bookworm, trixie, forky, sidm

m

a loadable module on every flavour - check lsmod, can be blacklisted

Build switch

CONFIG_GARP

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-07-19 (3 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.17%, higher than 6.5% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

net/802

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
2.6.27	5.10.259	29f28172afb2
2.6.27	5.15.210	973cf7c433d2
2.6.27	6.1.176	d8dcd14aa886
2.6.27	6.6.143	74e02121be1d
2.6.27	6.12.94	d4c86ea09ae3
2.6.27	6.18.36	04e22fefac1a
2.6.27	7.0.13	a11f1a671b13
2.6.27	7.1	16e408e607a9