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CVE-2026-68121
pppoe: reload header pointer after dev_hard_header()
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-68121 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 | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
pppoe_sendmsg() saves a pointer to the PPPoE header before calling dev_hard_header(). Device header callbacks are allowed to reallocate the skb head, invalidating pointers into it. This can happen when a send is blocked in copy_from_user() while the first non-Ethernet port is added to an empty team device. The team's delegated GRE header callback then expands the skb head. PPPoE subsequently writes six bytes through the stale pointer into the freed head. Reload the PPPoE header through the skb's network-header offset after device header creation. pskb_expand_head() updates that offset when it relocates the head.
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.
drivers/net/ppp/pppoe.c
- What this is
- PPP OVER ETHERNETMAINTAINERS section matched on drivers/net/ppp/pppoe.c · Orphan
- Kernel module
- pppoe
Check it on the machine
grep -wE 'CONFIG_PPP|CONFIG_PPPOE|CONFIG_PPPOL2TP|CONFIG_PPP_ASYNC|CONFIG_PPP_BSDCOMP|CONFIG_PPP_DEFLATE|CONFIG_PPP_MPPE|CONFIG_PPP_SYNC_TTY|CONFIG_PPTP' /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 pppoePrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- trixieMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x
- forky, sid, bookworm · linux-6.12Mnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_PPP, CONFIG_PPPOE, CONFIG_PPPOL2TP, CONFIG_PPP_ASYNC, CONFIG_PPP_BSDCOMP, CONFIG_PPP_DEFLATE, CONFIG_PPP_MPPE, CONFIG_PPP_SYNC_TTY, CONFIG_PPTP
- 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
- 2026-08-10 (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
- 0.30%, higher than 21.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 5.10.265 | 7a56e7c9b08e |
| 2.6.12 | 5.15.216 | 6eed5ae7887a |
| 2.6.12 | 6.1.183 | ba3409369c54 |
| 2.6.12 | 6.6.148 | e6493a4d1ee1 |
| 2.6.12 | 6.12.101 | 7e9fbd7f96bc |
| 2.6.12 | 6.18.42 | 6866abf59976 |
| 2.6.12 | 7.1.6 | bed4caecd723 |
| 2.6.12 | 7.2 | e9c238f6fe42 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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 bug is in pppoe_sendmsg(), reached only via the local sendmsg() syscall on a PF_PPPOX/PPPoE socket; it is not triggered by remote packet reception or in-kernel PPP transmit paths such as __pppoe_xmit().
- AC:LAttack complexity, low
- Exploitation requires a race between copy_from_user() blocking in sendmsg and changing team header_ops (e.g., adding the first non-Ethernet GRE port), which an attacker can drive with concurrent threads and retries rather than uncontrollable timing.
- PR:LPrivileges required, low
- PPPoE sockets can be created without special privileges, and configuring the team/GRE topology needed to trigger dev_hard_header() head expansion is achievable with CAP_NET_ADMIN inside an unprivileged user/network namespace (unshare -Urn).
- UI:NUser interaction, none
- No victim interaction is required; exploitation is fully attacker-driven through socket I/O and netlink/rtnl configuration of the team device.
- S:UScope, unchanged
- Impact is kernel heap corruption and privilege escalation within the same kernel security authority, not a cross-boundary escape such as guest-to-host VM breakout or IOMMU bypass.
- C:HConfidentiality impact, high
- Writing PPPoE header fields through a stale pointer after pskb_expand_head() frees the old skb head is a slab use-after-free; freed kmalloc objects can be reclaimed for sensitive data, enabling arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The post-dev_hard_header() memcpy/ph->length stores up to eight attacker-influenced bytes into freed skb head memory, providing a heap corruption primitive that can be developed into arbitrary kernel writes or code execution.
- A:HAvailability impact, high
- Use-after-free writes into freed slab memory commonly cause kernel oops/panic and can be triggered repeatedly via sendmsg, yielding persistent denial of service even when full exploitation is not attempted.