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CVE-2026-74668
packet: use consistent hard_header_len in TX_RING send 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-2026-74668 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
tpacket_snd() reads dev->hard_header_len independently for skb allocation and header construction in tpacket_fill_skb(). Concurrent netdevice reconfiguration can therefore make the reserved headroom smaller than the amount later pushed, or make copylen - hard_header_len negative. Snapshot hard_header_len once before processing ring frames and use it for the frame limit, headroom allocation, copy length, and skb construction. Pass the snapshot to tpacket_fill_skb(). The separate SOCK_DGRAM consistency problem between hard_header_len and header_ops->create is not addressed here.
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
- 0.13%, higher than 2.3% 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 |
|---|---|---|
| 2.6.31 | 5.10.267 | 9c7e8ff48c37 |
| 2.6.31 | 5.15.218 | 2a73b2c37ee3 |
| 2.6.31 | 6.1.185 | e79f59a8527a |
| 2.6.31 | 6.6.152 | d85d2fd54e90 |
| 2.6.31 | 6.12.104 | 016763e829ca |
| 2.6.31 | 6.18.45 | 27e068d1b35d |
| 2.6.31 | 7.1.9 | d48ea5c9c4c3 |
| 2.6.31 | 7.2 | 21b5953e7494 |
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 syscalls on an AF_PACKET socket with PACKET_TX_RING configured (sendmsg on mmap ring frames); it is not triggered by processing remotely received network traffic.
- AC:LAttack complexity, low
- An attacker can open the TX_RING socket and concurrently reconfigure the bound netdev (e.g., VLAN/bonding/macvlan changes) in a user+network namespace, controlling both sides of the hard_header_len race without depending on external timing.
- PR:LPrivileges required, low
- Exploitation requires CAP_NET_RAW to create AF_PACKET sockets and CAP_NET_ADMIN to change netdev hard_header_len; both are obtainable by an unprivileged user inside a user namespace without init-namespace root.
- UI:NUser interaction, none
- No victim interaction is required; the attacker triggers the bug using their own packet socket, TX_RING, and netdev reconfiguration threads.
- S:UScope, unchanged
- Impact is kernel heap corruption and local privilege escalation within the same kernel security domain; it does not constitute a VM escape, sandbox breakout, or IOMMU boundary bypass.
- C:HConfidentiality impact, high
- Racing hard_header_len can make skb_push exceed reserved headroom or skb_put use a negative length (huge unsigned), and subsequent skb_store_bits writes before skb->head or far past skb->tail, corrupting adjacent slab objects and enabling kernel memory disclosure.
- I:HIntegrity impact, high
- Inconsistent hard_header_len between skb allocation and tpacket_fill_skb causes out-of-bounds linear expansion and data writes in the skb buffer, yielding heap corruption primitives suitable for control-flow hijacking and local privilege escalation.
- A:HAvailability impact, high
- Corrupted skb_push/put operations invoke skb_under_panic or skb_over_panic (BUG), causing kernel oops/panic and reliable denial of service even when exploitation is not completed.