CVE-2026-45844
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
In the Linux kernel netfilter arp_tables subsystem, a vulnerability was found due to incorrect parsing of ARP packets for IEEE1394 (FireWire) interfaces. According to RFC 2734, ARP for IPv4-over-IEEE1394 omits the target hardware address field, causing the arp_packet_match() function to read wrong bytes when comparing addresses. This leads to incorrect filtering decisions – packets may be wrongly accepted or dropped. Additionally, mangling operations on these fields can cause packet corruption.
Risk Assessment
Organizations using IEEE1394 (FireWire) interfaces and arptables rules are exposed to incorrect ARP traffic filtering, which may result in network misbehavior, blocking legitimate traffic, or allowing malicious packets. Moreover, attempts to mangle ARP packets on these interfaces can lead to packet corruption.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit in the netfilter branch). Until the update is applied, avoid using arptables rules that reference the target hardware address or mangle ARP packets on IEEE1394 interfaces.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: netfilter: arp_tables: fix IEEE1394 ARP payload parsing Weiming Shi says: "arp_packet_match() unconditionally parses the ARP payload assuming two hardware addresses are present (source and target). However, IPv4-over-IEEE1394 ARP (RFC 2734) omits the target hardware address field, and arp_hdr_len() already accounts for this by returning a shorter length for ARPHRD_IEEE1394 devices. As a result, on IEEE1394 interfaces arp_packet_match() advances past a nonexistent target hardware address and reads the wrong bytes for both the target device address comparison and the target IP address. This causes arptables rules to match against garbage data, leading to incorrect filtering decisions: packets that should be accepted may be dropped and vice versa. The ARP stack in net/ipv4/arp.c (arp_create and arp_process) already handles this correctly by skipping the target hardware address for ARPHRD_IEEE1394. Apply the same pattern to arp_packet_match()." Mangle the original patch to always return 0 (no match) in case user matches on the target hardware address which is never present in IEEE1394. Note that this returns 0 (no match) for either normal and inverse match because matching in the target hardware address in ARPHRD_IEEE1394 has never been supported by arptables. This is intentional, matching on the target hardware address should never evaluate true for ARPHRD_IEEE1394. Moreover, adjust arpt_mangle to drop the packet too as AI suggests: In arpt_mangle, the logic assumes a standard ARP layout. Because IEEE1394 (FireWire) omits the target hardware address, the linear pointer arithmetic miscalculates the offset for the target IP address. This causes mangling operations to write to the wrong location, leading to packet corruption. To ensure safety, this patch drops packets (NF_DROP) when mangling is requested for these fields on IEEE1394 devices, as the current implementation cannot correctly map the FireWire ARP payload. This omits both mangling target hardware and IP address. Even if IP address mangling should be possible in IEEE1394, this would require to adjust arpt_mangle offset calculation, which has never been supported. Based on patch from Weiming Shi <[email protected]>.