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CVE-2026-52942
netfilter: nf_log: validate MAC header was set before dumping it
Published 2026-06-24 (4 months ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-52942 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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)
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/netfilter/nf_log_syslog.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_log_syslog
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_LOG_SYSLOG' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w nf_log_syslogPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NF_LOG_SYSLOG
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-06-24 (4 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.36 | 5.10.261 | 2e96e1bc9b4d |
| 2.6.36 | 5.15.210 | d704ee9c7bc6 |
| 2.6.36 | 6.1.176 | befb8968a2ab |
| 2.6.36 | 6.6.143 | 8a81e336da68 |
| 2.6.36 | 6.12.94 | c38d41134085 |
| 2.6.36 | 6.18.36 | af1b7699466f |
| 2.6.36 | 7.0.13 | 65ef7397eb9a |
| 2.6.36 | 7.1 | a84b6fedbc97 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | tracker |
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The vulnerable path is reached by local kernel interfaces: installing a netdev nftables log rule through nfnetlink and sending an AF_PACKET frame with PACKET_QDISC_BYPASS. It is not triggered directly by unauthenticated remote network packets.
- AC:LAttack complexity, low
- There is no race or fragile timing requirement; once the rule, egress hook, and packet socket option are set, sending a crafted AF_PACKET frame reliably reaches dump_mac_header() with an unset MAC header. The attacker controls the triggering packet path.
- PR:LPrivileges required, low
- The setup requires CAP_NET_ADMIN for nftables and CAP_NET_RAW for AF_PACKET, both namespace-relative and reachable by an unprivileged local user in user/network namespaces in a reasonable deployment where nf_log_all_netns permits netns logging. If only init_net logging is allowed, this rises to init-namespace admin, but the higher-severity reasonable user-namespace scenario is PR:L.
- UI:NUser interaction, none
- No victim action is required after the attacker has the needed local privileges. The attacker installs the rule and sends the packet themselves.
- S:UScope, unchanged
- The vulnerability affects kernel networking/logging resources within the same host security authority. It does not cross a VM, IOMMU, or other separate security boundary.
- C:HConfidentiality impact, high
- The bug reads bytes from roughly 64 KiB past skb->head and prints them into the kernel log, creating a repeatable kernel memory disclosure primitive. Although each log entry is bounded by dev->hard_header_len, repeated triggering and heap influence make high confidentiality impact defensible.
- I:NIntegrity impact, none
- The vulnerable operation is an out-of-bounds read used for logging MAC bytes. There is no write, object corruption, or control-flow modification primitive shown by the fix or reachable path.
- A:HAvailability impact, high
- The reported reproducer triggers a KASAN slab-out-of-bounds BUG/oops in dump_mac_header(), and hardened/debug deployments may panic on this condition. The trigger can also be repeated locally, so high availability impact is defensible.