CVE-2026-63868 net: garp: fix unsigned integer underflow in garp_pdu_parse_attr
An integer underflow in the Linux kernel GARP parser causes received Join/Leave events to be ignored, breaking VLAN registration and causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63868?
CVE-2026-63868 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: garp: fix unsigned integer underflow in garp_pdu_parse_attr
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.
Weakness: CWE-191
Which versions are affected by CVE-2026-63868?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-63868?
Apply the vendor's patch.
Is CVE-2026-63868 being exploited?
There is no known exploitation of CVE-2026-63868 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-63868, DEBIAN-CVE-2026-63868, GHSA-3pm7-r452-gg96, ROOT-OS-UBUNTU-2204-CVE-2026-63868, UBUNTU-CVE-2026-63868.