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CVE-2026-53003
pppoe: drop PFC frames
Published 2026-06-24 (4 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-2026-53003 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 | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
RFC 2516 Section 7 states that Protocol Field Compression (PFC) is NOT RECOMMENDED for PPPoE. In practice, pppd does not support negotiating PFC for PPPoE sessions, and the current PPPoE driver assumes an uncompressed (2-byte) protocol field. However, the generic PPP layer function ppp_input() is not aware of the negotiation result, and still accepts PFC frames. If a peer with a broken implementation or an attacker sends a frame with a compressed (1-byte) protocol field, the subsequent PPP payload is shifted by one byte. This causes the network header to be 4-byte misaligned, which may trigger unaligned access exceptions on some architectures. To reduce the attack surface, drop PPPoE PFC frames. Introduce ppp_skb_is_compressed_proto() helper function to be used in both ppp_generic.c and pppoe.c to avoid open-coding.
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/ppp_generic.c
drivers/net/ppp/pppoe.c
include/linux/ppp_defs.h
- What this is
- PPP PROTOCOL DRIVERS AND COMPRESSORSMAINTAINERS section matched on drivers/net/ppp/ppp_* · linux-ppp@vger.kernel.org · Orphan
- Kernel module
- ppp_generic
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 ppp_genericPrints 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, sidMnot 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
- 2026-06-24 (4 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.72%, higher than 52.9% 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 |
|---|---|---|
| 5.0 | 5.10.258 | cb3beef35ab5 |
| 5.0 | 5.15.209 | ba758fdf1399 |
| 5.0 | 6.1.175 | fcca1df05322 |
| 5.0 | 6.6.141 | 8a5e840babc5 |
| 5.0 | 6.12.91 | 49e41b60ccd1 |
| 5.0 | 6.18.33 | 0cab5d077dd1 |
| 5.0 | 7.0.10 | 2b5c3c040d02 |
| 5.0 | 7.1 | cc1ff87bce1c |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| 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 |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | 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:NAttack vector, network
- Crafted PPPoE session frames reach the vulnerable path through the kernel receive path for ETH_P_PPP_SES network packets. A malicious PPPoE peer or network attacker able to send matching session frames can trigger it remotely over the network interface.
- AC:LAttack complexity, low
- The trigger is a single compressed PPP protocol field in an otherwise valid PPPoE session frame, with no race or attacker-uncontrolled timing. On strict-alignment architectures used in plausible PPPoE deployments, the resulting misalignment deterministically reaches fault-prone network-header parsing.
- PR:NPrivileges required, none
- The attacker only needs to transmit crafted PPPoE frames to an existing session and does not need local privileges or authenticated access on the victim. Local CAP_NET_ADMIN may be needed to configure PPPoE, but that is not a privilege required by the packet sender.
- UI:NUser interaction, none
- No victim interaction is required once the target is running a PPPoE session. The malicious frame is processed asynchronously by the network receive path.
- S:UScope, unchanged
- The impact is within the kernel/network stack security authority of the vulnerable system. There is no VM, sandbox, or other separate security scope crossed.
- C:NConfidentiality impact, none
- The bug shifts packet alignment and can cause unaligned access exceptions, but it does not expose kernel memory or provide an information disclosure primitive. The skb push writes within packet headroom and is not an arbitrary read condition.
- I:NIntegrity impact, none
- The issue does not provide attacker-controlled modification of kernel memory or data structures. Its demonstrated and intended impact is malformed alignment leading to faulting packet processing, not integrity compromise.
- A:HAvailability impact, high
- Misaligned network headers can trigger unaligned access exceptions and kernel oops/panic on strict-alignment architectures. The crafted frame can be sent repeatedly, making system availability impact high.