# CVE-2026-52942: netfilter: nf_log: validate MAC header was set before dumping it

Status: published. Published: 2026-06-24. Updated: 2026-11-10.

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)

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < 2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < d704ee9c7bc68a161684c51a7ac05b446dcf38d4 (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < befb8968a2abdfa948d5600ea7f7a509a292a590 (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < 8a81e336da685423f5b64aac4d571e63d674c52a (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < c38d41134085193efd5b237cf513ad5b3421a60d (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < af1b7699466f6556b351fa25d3dc870abfb5d310 (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < 65ef7397eb9a296e91839f5fd10be96f23d332e7 (affected, git); ≥ 7eb9282cd0efac08b8377cbd5037ba297c77e3f7; < a84b6fedbc97078788be78dbdd7517d143ad1a77 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.36 (affected); ≥ 0; < 2.6.36 (unaffected, semver); ≥ 5.10.261; ≤ 5.10.* (unaffected, semver); ≥ 5.15.210; ≤ 5.15.* (unaffected, semver); ≥ 6.1.176; ≤ 6.1.* (unaffected, semver); ≥ 6.6.143; ≤ 6.6.* (unaffected, semver); ≥ 6.12.94; ≤ 6.12.* (unaffected, semver); ≥ 6.18.36; ≤ 6.18.* (unaffected, semver); ≥ 7.0.13; ≤ 7.0.* (unaffected, semver); ≥ 7.1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 TM MFP - GNU/Linux subsystem: ≥ 0; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CVSS 3.1: 7.1 (high); CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H; source: CNA: Linux

- CISA KEV: No listing in collected sources

- EPSS: 0.13% as of 2026-11-09; percentile 2.76%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/2e96e1bc9b4d5450e6c33f078e19a9bc1dda6c0b (CNA: Linux)

- https://git.kernel.org/stable/c/d704ee9c7bc68a161684c51a7ac05b446dcf38d4 (CNA: Linux)

- https://git.kernel.org/stable/c/befb8968a2abdfa948d5600ea7f7a509a292a590 (CNA: Linux)

- https://git.kernel.org/stable/c/8a81e336da685423f5b64aac4d571e63d674c52a (CNA: Linux)

- https://git.kernel.org/stable/c/c38d41134085193efd5b237cf513ad5b3421a60d (CNA: Linux)

- https://git.kernel.org/stable/c/af1b7699466f6556b351fa25d3dc870abfb5d310 (CNA: Linux)

- https://git.kernel.org/stable/c/65ef7397eb9a296e91839f5fd10be96f23d332e7 (CNA: Linux)

- https://git.kernel.org/stable/c/a84b6fedbc97078788be78dbdd7517d143ad1a77 (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-784472.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-52942; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-52942; retrieved 2026-11-10; source updated Not reported

Revision: 90270354798545bcae12698bc1f55eed2a8cbf9b059fbb21ac5ec78596504721

Canonical: https://y2.dev/cve/CVE-2026-52942

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