Medium [CVE-2026-63868] fix unsigned integer underflow in garp_pdu_parse_attr
This medium-severity Red Hat Linux advisory covers CVE-2026-63868 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8.
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Summary
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. A flaw was found in the Linux kernel's Generic Attribute Registration Protocol (GARP) network component.
A remote attacker could send specially crafted GARP attributes, leading to an unsigned integer underflow during attribute parsing. This underflow causes the system to incorrectly process attribute lengths, resulting in legitimate GARP Join/Leave events being ignored.
The primary impact is a denial of service, disrupting network functionalities that rely on GARP, such as GVRP VLAN registration.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative. Check it before change work.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists. Confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That does not mean no fix exists. Read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 7 days ago·verify at source
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