{"id":"CVE-2026-52942","summary":"netfilter: nf_log: validate MAC header was set before dumping it","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nf_log: validate MAC header was set before dumping it\n\nThe fallback path of dump_mac_header() guards the MAC header access\nonly with \"skb-\u003emac_header != skb-\u003enetwork_header\", without checking\nskb_mac_header_was_set(). When the MAC header is unset, mac_header is\n0xffff, so the test passes and skb_mac_header(skb) returns\nskb-\u003ehead + 0xffff, ~64 KiB past the buffer; the loop then reads\ndev-\u003ehard_header_len bytes out of bounds into the kernel log.\n\nThis is reachable via the netdev logger: nf_log_unknown_packet() calls\ndump_mac_header() unconditionally, and an skb sent through AF_PACKET\nwith PACKET_QDISC_BYPASS reaches the egress hook with mac_header still\nunset (__dev_queue_xmit(), which would reset it, is bypassed).\n\nAdd the skb_mac_header_was_set() check the ARPHRD_ETHER path already\nuses, and replace the open-coded MAC header length test with\nskb_mac_header_len(). Only skbs with an unset MAC header are affected;\nvalid ones are dumped as before.\n\n BUG: KASAN: slab-out-of-bounds in dump_mac_header (net/netfilter/nf_log_syslog.c:831)\n Read of size 1 at addr ffff88800ea49d3f by task exploit/148\n Call Trace:\n  kasan_report (mm/kasan/report.c:595)\n  dump_mac_header (net/netfilter/nf_log_syslog.c:831)\n  nf_log_netdev_packet (net/netfilter/nf_log_syslog.c:938 net/netfilter/nf_log_syslog.c:963)\n  nf_log_packet (net/netfilter/nf_log.c:260)\n  nft_log_eval (net/netfilter/nft_log.c:60)\n  nft_do_chain (net/netfilter/nf_tables_core.c:285)\n  nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:307)\n  nf_hook_slow (net/netfilter/core.c:619)\n  nf_hook_direct_egress (net/packet/af_packet.c:257)\n  packet_xmit (net/packet/af_packet.c:280)\n  packet_sendmsg (net/packet/af_packet.c:3114)\n  __sys_sendto (net/socket.c:2265)","modified":"2026-07-26T03:32:00.361382272Z","published":"2026-06-24T07:14:30.610Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52942.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/65ef7397eb9a296e91839f5fd10be96f23d332e7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8a81e336da685423f5b64aac4d571e63d674c52a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a84b6fedbc97078788be78dbdd7517d143ad1a77"},{"type":"WEB","url":"https://git.kernel.org/stable/c/af1b7699466f6556b351fa25d3dc870abfb5d310"},{"type":"WEB","url":"https://git.kernel.org/stable/c/befb8968a2abdfa948d5600ea7f7a509a292a590"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c38d41134085193efd5b237cf513ad5b3421a60d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d704ee9c7bc68a161684c51a7ac05b446dcf38d4"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52942.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-52942"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"7eb9282cd0efac08b8377cbd5037ba297c77e3f7"},{"fixed":"2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b"},{"fixed":"d704ee9c7bc68a161684c51a7ac05b446dcf38d4"},{"fixed":"befb8968a2abdfa948d5600ea7f7a509a292a590"},{"fixed":"8a81e336da685423f5b64aac4d571e63d674c52a"},{"fixed":"c38d41134085193efd5b237cf513ad5b3421a60d"},{"fixed":"af1b7699466f6556b351fa25d3dc870abfb5d310"},{"fixed":"65ef7397eb9a296e91839f5fd10be96f23d332e7"},{"fixed":"a84b6fedbc97078788be78dbdd7517d143ad1a77"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-52942.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.36"},{"fixed":"5.10.261"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.210"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.176"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.143"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.94"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.36"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.13"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-52942.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H"}]}