CVE-2026-52942

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> netfilter: nf_log: validate MAC header was set before dumping it<br /> <br /> The fallback path of dump_mac_header() guards the MAC header access<br /> only with "skb-&gt;mac_header != skb-&gt;network_header", without checking<br /> skb_mac_header_was_set(). When the MAC header is unset, mac_header is<br /> 0xffff, so the test passes and skb_mac_header(skb) returns<br /> skb-&gt;head + 0xffff, ~64 KiB past the buffer; the loop then reads<br /> dev-&gt;hard_header_len bytes out of bounds into the kernel log.<br /> <br /> This is reachable via the netdev logger: nf_log_unknown_packet() calls<br /> dump_mac_header() unconditionally, and an skb sent through AF_PACKET<br /> with PACKET_QDISC_BYPASS reaches the egress hook with mac_header still<br /> unset (__dev_queue_xmit(), which would reset it, is bypassed).<br /> <br /> Add the skb_mac_header_was_set() check the ARPHRD_ETHER path already<br /> uses, and replace the open-coded MAC header length test with<br /> skb_mac_header_len(). Only skbs with an unset MAC header are affected;<br /> valid ones are dumped as before.<br /> <br /> BUG: KASAN: slab-out-of-bounds in dump_mac_header (net/netfilter/nf_log_syslog.c:831)<br /> Read of size 1 at addr ffff88800ea49d3f by task exploit/148<br /> Call Trace:<br /> kasan_report (mm/kasan/report.c:595)<br /> dump_mac_header (net/netfilter/nf_log_syslog.c:831)<br /> nf_log_netdev_packet (net/netfilter/nf_log_syslog.c:938 net/netfilter/nf_log_syslog.c:963)<br /> nf_log_packet (net/netfilter/nf_log.c:260)<br /> nft_log_eval (net/netfilter/nft_log.c:60)<br /> nft_do_chain (net/netfilter/nf_tables_core.c:285)<br /> nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:307)<br /> nf_hook_slow (net/netfilter/core.c:619)<br /> nf_hook_direct_egress (net/packet/af_packet.c:257)<br /> packet_xmit (net/packet/af_packet.c:280)<br /> packet_sendmsg (net/packet/af_packet.c:3114)<br /> __sys_sendto (net/socket.c:2265)