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Fencer Vulns
high 7.8

CVE-2026-68398 json

ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF

published 2026-08-10 2 mo ago modified 2026-10-19 20 d ago also EUVD-2026-55584

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF

pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:

l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan)

It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences.

The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree():

close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)

For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU.

The bug is reachable by an unprivileged user.

Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.

Patch / fix

  • Linux Linux 3.3, 3.17, 4.5, 4.10, 4.15, 5.15.216, 6.1.183, 6.6.148, 6.12.101, 6.18.42, 7.1.6, 7.2
  • linux Debian 12 6.1.187-1
  • linux Debian 13 6.12.101-1
  • linux Debian 14 7.1.6-1
  • linux-6.12 Debian 12 6.12.101-1~deb12u1

debian advisories DEBIAN-CVE-2026-68398

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-147.147
  • linux Ubuntu 26.04 LTS 7.0.0-38.38
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1067.70
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1014.14
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1071.79

ubuntu advisories UBUNTU-CVE-2026-68398

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-64kb SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS, SLE High Performance Computing 15 SP5-ESPOS 5.14.21-150500.55.189.1
  • kernel-syms SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-source SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1
  • kernel-default SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +3 more 5.14.21-150500.55.189.1
  • kernel-obs-build SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE High Performance Computing 15 SP5-LTSS +1 more 5.14.21-150500.55.189.1
  • kernel-default-base SLES for SAP 15 SP5, SLES 15 SP5-LTSS, SLE Micro 5.5 +2 more 5.14.21-150500.55.189.1.150500.6.87.4
  • kernel-64kb SLE Module for Basesystem 15 SP7 6.4.0-150700.53.81.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.81.1

suse advisories SUSE-SU-2026:4595-1SUSE-SU-2026:4254-1SUSE-SU-2026:4369-1SUSE-SU-2026:4347-1SUSE-SU-2026:4284-1SUSE-SU-2026:23887-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.38.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.38.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.38.1

opensuse advisories openSUSE-SU-2026:21910-1

  • kernel Rocky Linux 10 6.12.0-211.72.1.el10_2

rocky linux advisories RLSA-2026:93413

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-68398 updated cvss 7.8

kernel: Linux kernel: PPP over L2TP Use-After-Free vulnerability

  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux kernel-modules-internal 6.12.0-211.72.1.el10_2 Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.72.1.el10_2, perf 6.12.0-211.72.1.el10_2, rtla 6.12.0-211.72.1.el10_2, python3-perf 6.12.0-211.72.1.el10_2, kernel-devel-matched 6.12.0-211.72.1.el10_2, kernel-64k-devel-matched 6.12.0-211.72.1.el10_2, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.72.1.el10_2, kernel-64k 6.12.0-211.72.1.el10_2, kernel-core 6.12.0-211.72.1.el10_2, kernel-tools 6.12.0-211.72.1.el10_2, kernel-modules 6.12.0-211.72.1.el10_2, kernel-64k-core 6.12.0-211.72.1.el10_2, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.72.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.72.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.72.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.72.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.72.1.el10_2 Red Hat Enterprise Linux Hidden (v. 10) kernel-modules-internal 6.12.0-211.72.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.72.1.el10_2 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.72.1.el10_2, kernel-rt-64k 6.12.0-211.72.1.el10_2, kernel-rt-core 6.12.0-211.72.1.el10_2, kernel-rt-modules 6.12.0-211.72.1.el10_2, kernel-rt-64k-core 6.12.0-211.72.1.el10_2, kernel-rt-debug-core 6.12.0-211.72.1.el10_2, +14 more
    +1 more products
    Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.72.1.el10_2, kernel-rt-core 6.12.0-211.72.1.el10_2, kernel-rt-modules 6.12.0-211.72.1.el10_2, kernel-rt-debug-core 6.12.0-211.72.1.el10_2, kernel-rt-modules-core 6.12.0-211.72.1.el10_2, kernel-rt-debug-modules 6.12.0-211.72.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:93413
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.