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CVE-2026-74667
net/packet: reset the MAC header on the packet-socket transmit path
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem net/packet. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74667 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
packet_parse_headers() resets the MAC header only for a SOCK_RAW frame whose socket did not bind a protocol. A protocol-bound SOCK_RAW socket, any SOCK_DGRAM frame, and the legacy SOCK_PACKET path therefore leave skb->mac_header unset here. For frames sent via __dev_queue_xmit() this is harmless: it resets the MAC header unconditionally. But the packet-socket PACKET_QDISC_BYPASS path uses dev_direct_xmit(), which does not, so the frame reaches ndo_start_xmit() with the MAC header unset. A driver that reads eth_hdr(skb) on transmit then dereferences skb->head + (u16)~0, an out-of-bounds access ~64 KiB past the head -- the same class fixed for one consumer in commit f5089008f90c ("macsec: do not read an unset MAC header in macsec_encrypt()"). packet_parse_headers() runs only on the transmit path, where skb->data points at the start of the L2 header for every packet-socket type regardless of its length: SOCK_RAW and SOCK_PACKET carry a user-supplied header and SOCK_DGRAM has one built by dev_hard_header(). Reset the MAC header unconditionally, mirroring __dev_queue_xmit(), so the frame is anchored on the bypass path too. Found by 0sec (https://0sec.ai) using automated source analysis; verified against source and matched to the macsec KASAN report in f5089008f90c. Compile-tested.
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/packet/af_packet.c
- What this is
- PACKET SOCKETSMAINTAINERS section matched on net/packet/af_packet.c · Maintained
Check it on the machine
grep -w CONFIG_PACKET /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.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_PACKET
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
- 2026-08-22 (2 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.14%, higher than 2.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/packet
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.1 | 5.10.265 | 1e43a1d66615 |
| 5.1 | 5.15.216 | 4057853a91fb |
| 5.1 | 6.1.183 | 2610ed4e86a4 |
| 5.1 | 6.6.152 | b47ba8fe6e1d |
| 5.1 | 6.12.104 | 284f3e7a3f1a |
| 5.1 | 6.18.45 | 971aa7d99242 |
| 5.1 | 7.1.9 | fdd4d7d52358 |
| 5.1 | 7.2 | c2707480cfbf |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 flaw is reached only via local AF_PACKET transmit syscalls (sendmsg on SOCK_DGRAM/bound SOCK_RAW with PACKET_QDISC_BYPASS); remote network input cannot trigger packet_parse_headers() on this TX path.
- AC:LAttack complexity, low
- The attacker controls socket type, enables PACKET_QDISC_BYPASS via setsockopt, selects a vulnerable netdev (macsec/macvlan/tap), and sends frames to reliably hit dev_direct_xmit() without races or external victim state.
- PR:LPrivileges required, low
- packet_create() requires CAP_NET_RAW, which unprivileged users commonly obtain inside user+network namespaces (unshare -Urn) per kernel capability rules, not solely real root in the init namespace.
- UI:NUser interaction, none
- Exploitation requires only the attacker opening a packet socket, enabling bypass, and transmitting; no victim user action such as opening files or mounting filesystems is needed.
- S:UScope, unchanged
- Impact is kernel heap/slab disclosure and transmit-time corruption within the same kernel security authority; it is not a VM escape, IOMMU bypass, or other cross-boundary scope change.
- C:HConfidentiality impact, high
- Unset mac_header makes eth_hdr(skb) a large out-of-bounds kernel memory read (~64 KiB past skb->head); macsec KASAN confirmed slab data leakage and bytes can be emitted on the wire in the frame.
- I:HIntegrity impact, high
- Affected TX drivers consume the bogus eth_hdr() pointer to modify skbs (e.g., macsec memmove of OOB MAC bytes into the frame, vxlan header rewrites), giving attacker-influenced corruption beyond a pure read.
- A:HAvailability impact, high
- The invalid mac_header dereference can fault or trigger KASAN/driver failures during ndo_start_xmit(), causing kernel oops/panic or repeated transmit failure on the bypass path.