CVE-2026-98287

What the bug is

In pppoatm_send(), LLC encapsulation checks whether there is sufficient headroom for the 4-byte LLC header, but does not ensure that the skb header is writable. Normal transmit packets passing through ppp_start_xmit() have their header unshared via skb_cow_head(). However, packets can also reach pppoatm_send() via PPP channel bridging (PPPIOCBRIDGECHAN) without going through ppp_start_xmit(). Use skb_cow_head() to ensure both sufficient headroom and a writable header before pushing the LLC header. While at it: - Call pskb_may_pull(skb, 1) before inspecting skb->data[0] to prevent out-of-bounds reads on zero-length or non-linear frames (e.g. from bridging). - Defer SC_COMP_PROT protocol compression until after pppoatm_may_send() succeeds. This eliminates the temporary skb allocation on admission failure and completely removes the fragile "undo" heuristic at the nospace label, avoiding any risk of reading uninitialized headroom or performing an unbalanced skb_push().

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/atm/pppoatm.c

What this is

PPP OVER ATM (RFC 2364)MAINTAINERS section matched on net/atm/pppoatm.c · Maintained

Kernel module

pppoatm

Check it on the machine

grep -wE 'CONFIG_ATM|CONFIG_PPPOATM' /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 pppoatm

Prints 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
• trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64, s390x/s390x

M

a module where it is built at all; some flavours do not build it

Build switches

CONFIG_ATM, CONFIG_PPPOATM

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

2026-10-06 (13 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.18%, higher than 7.1% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

net/atm

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
5.11	5.15.222	208ccc4d08b1
5.11	6.1.189	e6cd1bba7d11
5.11	6.6.158	ffc448eb54f5
5.11	6.12.112	8e66c5969acd
5.11	6.18.54	e2f5529b0016
5.11	7.2.8	30992fe39e65
5.11	7.3	ecc7253683a3

Debian advisories