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CVE-2026-74582
packet: use consistent hard_header_len in non-ring send paths
Published 2026-08-21 (2 months ago) by the Linux kernel CNA. Subsystem include/linux. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74582 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_snd() reads dev->hard_header_len multiple times while allocating and constructing an skb. Device reconfiguration can change this value concurrently, for example through bonding device type changes. For SOCK_RAW, packet_snd() can save a larger value in reserve and later allocate headroom using a smaller value. Moving skb->data back by reserve then places it before skb->head, and the following copy from userspace can attempt an out-of-bounds write. packet_sendmsg_spkt() has the same issue because it calculates its reservation and header offset from separate reads before dropping the RCU read lock to allocate the skb. Add LL_RESERVED_SPACE_EX() for callers that already saved a header length. Read hard_header_len once in packet_snd() and use it for allocation and construction. In packet_sendmsg_spkt(), preserve the allocation-time value through the device lookup retry. 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.
include/linux/netdevice.h
net/packet/af_packet.c
- What this is
- NETWORKING DRIVERSMAINTAINERS section matched on include/linux/netdev* · netdev@vger.kernel.org · 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
- 2026-08-21 (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
- 0.12%, higher than 1.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/linux
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.17 | 5.10.267 | bcd4df60ac94 |
| 4.17 | 5.15.218 | 78a47127e33c |
| 4.17 | 6.1.185 | 142e287b3a25 |
| 4.17 | 6.6.152 | 91f041451f96 |
| 4.17 | 6.12.104 | 905275629096 |
| 4.17 | 6.18.45 | 5bb10753d428 |
| 4.17 | 7.1.9 | b06b6fce6d7d |
| 4.17 | 7.2 | 03390aa32e66 |
| 4.4.133 | 0 | 0 |
| 4.9.103 | 0 | 0 |
| 4.14.44 | 0 | 0 |
| 4.16.12 | 0 | 0 |
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 in packet_snd() and packet_sendmsg_spkt() on the local AF_PACKET sendmsg() transmit path; it is not triggered by processing remotely received network traffic or pre-authentication network services.
- AC:LAttack complexity, low
- An attacker in a user+network namespace can open an AF_PACKET SOCK_RAW socket and concurrently reconfigure the bound netdev (bonding/VLAN/macvlan/team) to change hard_header_len, controlling both sides of the race without 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 sendmsg calls and concurrent 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 place skb->data before skb->head, and skb_copy_datagram_from_iter/memcpy_from_msg then writes attacker-controlled data outside the skb buffer, corrupting adjacent slab objects and enabling kernel memory disclosure.
- I:HIntegrity impact, high
- Inconsistent hard_header_len between skb allocation and header adjustment causes out-of-bounds kernel heap writes of attacker-controlled packet data, yielding corruption primitives suitable for control-flow hijacking and local privilege escalation.
- A:HAvailability impact, high
- Out-of-bounds skb buffer writes corrupt kmalloc metadata and can trigger kernel oops/panic, causing reliable denial of service even when full exploitation is not completed.