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Fencer Vulns
critical 9.8

CVE-2026-63994 in the critical feed json

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

published 2026-07-19 3 mo ago modified 2026-10-19 20 d ago also EUVD-2026-45567

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

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

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head.

Fix this possible UAF by initializing the local variables after the skb_cow() call.

Remove skb_reset_network_header() calls which were not needed.

Patch / fix

  • Linux Linux 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35, 7.0.12, 7.1
  • linux Debian 12 6.1.176-1
  • linux Debian 13 6.12.94-1
  • linux Debian 14 7.0.12-1

debian advisories DEBIAN-CVE-2026-63994

  • linux Ubuntu 22.04 LTS 5.15.0-194.204
  • linux Ubuntu 24.04 LTS 6.8.0-142.142
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1116.123
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1065.68
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1117.127
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1069.77

ubuntu advisories UBUNTU-CVE-2026-63994

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 RHEL 9 5.14.0-687.55.1.el9_8
  • rv RHEL 9 5.14.0-687.55.1.el9_8
  • perf RHEL 9 5.14.0-687.55.1.el9_8
  • rtla RHEL 9 5.14.0-687.55.1.el9_8
  • libperf RHEL 9 5.14.0-687.55.1.el9_8
  • kernel-rt RHEL 9 5.14.0-687.55.1.el9_8
  • kernel-64k RHEL 9 5.14.0-687.55.1.el9_8
  • kernel-core RHEL 9 5.14.0-687.55.1.el9_8

red hat advisories RHSA-2026:76739RHSA-2026:75747RHSA-2026:75746

  • kernel-livepatch-SLE16_Update_5 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 12-160000.1.1
  • kernel-livepatch-SLE16_Update_9 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 8-160000.1.1
  • kernel-livepatch-SLE16_Update_0 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 19-160000.4.3
  • kernel-livepatch-MICRO-6-0-RT_Update_18 Linux Micro 6.1, Linux Micro 6.0 11-1.1
  • kernel-livepatch-MICRO-6-0-RT_Update_15 Linux Micro 6.1, Linux Micro 6.0 12-1.1
  • kernel-livepatch-MICRO-6-0-RT_Update_14 Linux Micro 6.1, Linux Micro 6.0 13-1.1
  • kernel-livepatch-MICRO-6-0-RT_Update_13 Linux Micro 6.1, Linux Micro 6.0 13-1.1
  • kernel-livepatch-MICRO-6-0-RT_Update_12 Linux Micro 6.1, Linux Micro 6.0 17-1.1

suse advisories SUSE-SU-2026:24107-1SUSE-SU-2026:24108-1SUSE-SU-2026:24174-1SUSE-SU-2026:24175-1SUSE-SU-2026:24106-1SUSE-SU-2026:24173-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.37.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.37.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.37.1

opensuse advisories openSUSE-SU-2026:21555-1

  • kernel AlmaLinux 10 6.12.0-211.63.1.el10_2
  • rv AlmaLinux 10 6.12.0-211.63.1.el10_2
  • perf AlmaLinux 10 6.12.0-211.63.1.el10_2
  • rtla AlmaLinux 10 6.12.0-211.63.1.el10_2
  • libperf AlmaLinux 10 6.12.0-211.63.1.el10_2
  • kernel-rt AlmaLinux 10 6.12.0-211.63.1.el10_2
  • kernel-64k AlmaLinux 10 6.12.0-211.63.1.el10_2
  • kernel-core AlmaLinux 10 6.12.0-211.63.1.el10_2

almalinux advisories ALSA-2026:76738ALSA-2026:75746ALSA-2026:75747

  • kernel-rt Rocky Linux 8 4.18.0-553.171.1.rt7.512.el8_10
  • kernel Rocky Linux 8 4.18.0-553.171.1.el8_10

rocky linux advisories RLSA-2026:75746RLSA-2026:75747

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-2026-63994 updated cvss 7.0

kernel: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more
    under investigation
  • Red Hat Enterprise Linux kernel-modules-internal 6.12.0-211.63.1.el10_2
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.55.1.el9_8, perf 5.14.0-687.55.1.el9_8, rtla 5.14.0-687.55.1.el9_8, python3-perf 5.14.0-687.55.1.el9_8, kernel-devel-matched 5.14.0-687.55.1.el9_8, kernel-64k-devel-matched 5.14.0-687.55.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:76739
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.63.1.el10_2, perf 6.12.0-211.63.1.el10_2, rtla 6.12.0-211.63.1.el10_2, python3-perf 6.12.0-211.63.1.el10_2, kernel-devel-matched 6.12.0-211.63.1.el10_2, kernel-64k-devel-matched 6.12.0-211.63.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.171.1.el8_10, kernel 4.18.0-553.171.1.el8_10, bpftool 4.18.0-553.171.1.el8_10, kernel-core 4.18.0-553.171.1.el8_10, kernel-tools 4.18.0-553.171.1.el8_10, python3-perf 4.18.0-553.171.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:75747
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.55.1.el9_8, kernel-64k 5.14.0-687.55.1.el9_8, kernel-core 5.14.0-687.55.1.el9_8, kernel-tools 5.14.0-687.55.1.el9_8, kernel-modules 5.14.0-687.55.1.el9_8, kernel-64k-core 5.14.0-687.55.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:76739
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.63.1.el10_2, kernel-64k 6.12.0-211.63.1.el10_2, kernel-core 6.12.0-211.63.1.el10_2, kernel-tools 6.12.0-211.63.1.el10_2, kernel-modules 6.12.0-211.63.1.el10_2, kernel-64k-core 6.12.0-211.63.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:76738
show 11 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.55.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.55.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.55.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.55.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.55.1.el9_8
    fixed: vendor fix RHSA-2026:76739
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.63.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.63.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.63.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.63.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.63.1.el10_2
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.171.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.171.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.171.1.el8_10
    fixed: vendor fix RHSA-2026:75747
  • Red Hat Enterprise Linux Hidden (v. 10) kernel-modules-internal 6.12.0-211.63.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.63.1.el10_2
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-kvm 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-core 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-modules 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-debug-kvm 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-debug-core 4.18.0-553.171.1.rt7.512.el8_10, +4 more
    fixed: vendor fix RHSA-2026:75746
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.55.1.el9_8, kernel-rt-64k 5.14.0-687.55.1.el9_8, kernel-rt-core 5.14.0-687.55.1.el9_8, kernel-rt-modules 5.14.0-687.55.1.el9_8, kernel-rt-64k-core 5.14.0-687.55.1.el9_8, kernel-rt-debug-core 5.14.0-687.55.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:76739
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.63.1.el10_2, kernel-rt-64k 6.12.0-211.63.1.el10_2, kernel-rt-core 6.12.0-211.63.1.el10_2, kernel-rt-modules 6.12.0-211.63.1.el10_2, kernel-rt-64k-core 6.12.0-211.63.1.el10_2, kernel-rt-debug-core 6.12.0-211.63.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.55.1.el9_8, kernel-rt-core 5.14.0-687.55.1.el9_8, kernel-rt-modules 5.14.0-687.55.1.el9_8, kernel-rt-debug-core 5.14.0-687.55.1.el9_8, kernel-rt-modules-core 5.14.0-687.55.1.el9_8, kernel-rt-debug-modules 5.14.0-687.55.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:76739
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.63.1.el10_2, kernel-rt-core 6.12.0-211.63.1.el10_2, kernel-rt-modules 6.12.0-211.63.1.el10_2, kernel-rt-debug-core 6.12.0-211.63.1.el10_2, kernel-rt-modules-core 6.12.0-211.63.1.el10_2, kernel-rt-debug-modules 6.12.0-211.63.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:76738
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-core 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-modules 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-debug-core 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-debug-modules 4.18.0-553.171.1.rt7.512.el8_10, kernel-rt-modules-extra 4.18.0-553.171.1.rt7.512.el8_10, +2 more
    fixed: vendor fix RHSA-2026:75746
  • 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
yes
Technical impact
total
Assessed
23 d ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/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.