Skip to content
Fencer Vulns
high 7.8

CVE-2026-64009 json

xfrm: Check for underflow in xfrm_state_mtu

published 2026-07-19 3 mo ago modified 2026-10-19 20 d ago also EUVD-2026-45582

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 3%
public exploits
0
none known

Summary

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

xfrm: Check for underflow in xfrm_state_mtu

Leo Lin reported OOB write issue in esp component:

xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned modulo-2^32 space using an attacker-influenced "header_len + authsize + net_adj" subtracted from a small "mtu" argument. A nobody user can install an IPv4 ESP tunnel SA with a large authentication key (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc), configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a large value. When a single UDP datagram is then sent through the tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and esp_output() consumes it as a signed int via:

padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached)) esp.tfclen = padto - skb->len (assigned to int)

esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t when passed to memset() inside esp_output_fill_trailer(), producing a ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as "Write of size 18446744073709551537 at addr ffff888...".

Check for underflow and return 1. This causes the sendmsg attempt to fail with ENETUNREACH.

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-2026-64009

  • linux Ubuntu 22.04 LTS 5.15.0-198.208
  • linux Ubuntu 24.04 LTS 6.8.0-146.146
  • linux Ubuntu 26.04 LTS 7.0.0-28.28
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1117.124
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1066.69
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1009.9
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1118.128
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1070.78

ubuntu advisories UBUNTU-CVE-2026-64009

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 SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-syms SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.53.84.1
  • kernel-source SLE Module for Development Tools 15 SP7, SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-default SLE Workstation Extension 15 SP7, SLE Module for Legacy 15 SP7, SLE Module for Basesystem 15 SP7 +2 more 6.4.0-150700.53.84.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1
  • kernel-obs-build SLE Module for Development Tools 15 SP7 6.4.0-150700.53.84.1
  • kernel-default-base SLE Module for Basesystem 15 SP7 6.4.0-150700.53.84.1.150700.17.47.1

suse advisories SUSE-SU-2026:4706-1SUSE-SU-2026:4687-1SUSE-SU-2026:4640-1SUSE-SU-2026:24316-1SUSE-SU-2026:24315-1SUSE-SU-2026:24181-1

  • kernel-rt openSUSE Leap 16.0 6.12.0-160000.39.1
  • dtb-aarch64 openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-64kb openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-syms openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-azure openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-obs-qa openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-source openSUSE Leap 16.0 6.12.0-160000.39.1
  • kernel-default openSUSE Leap 16.0 6.12.0-160000.39.1

opensuse advisories openSUSE-SU-2026:22091-1

  • kernel AlmaLinux 8 4.18.0-553.176.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.176.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.176.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.176.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.176.1.el8_10

almalinux advisories ALSA-2026:85773ALSA-2026:86033ALSA-2026:85321

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-2026-64009 updated cvss 7.0

kernel: xfrm: Check for underflow in xfrm_state_mtu

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more 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 6.12.0-211.67.1.el10_2
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-687.59.1.el9_8, perf 5.14.0-687.59.1.el9_8, rtla 5.14.0-687.59.1.el9_8, python3-perf 5.14.0-687.59.1.el9_8, kernel-devel-matched 5.14.0-687.59.1.el9_8, kernel-64k-devel-matched 5.14.0-687.59.1.el9_8, +7 more
    fixed: vendor fix RHSA-2026:86033
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-211.67.1.el10_2, perf 6.12.0-211.67.1.el10_2, rtla 6.12.0-211.67.1.el10_2, python3-perf 6.12.0-211.67.1.el10_2, kernel-devel-matched 6.12.0-211.67.1.el10_2, kernel-64k-devel-matched 6.12.0-211.67.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.176.1.el8_10, kernel 4.18.0-553.176.1.el8_10, bpftool 4.18.0-553.176.1.el8_10, kernel-core 4.18.0-553.176.1.el8_10, kernel-tools 4.18.0-553.176.1.el8_10, python3-perf 4.18.0-553.176.1.el8_10, +15 more
    fixed: vendor fix RHSA-2026:85773
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-687.59.1.el9_8, kernel-64k 5.14.0-687.59.1.el9_8, kernel-core 5.14.0-687.59.1.el9_8, kernel-tools 5.14.0-687.59.1.el9_8, kernel-modules 5.14.0-687.59.1.el9_8, kernel-64k-core 5.14.0-687.59.1.el9_8, +27 more
    fixed: vendor fix RHSA-2026:86033
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-211.67.1.el10_2, kernel-64k 6.12.0-211.67.1.el10_2, kernel-core 6.12.0-211.67.1.el10_2, kernel-tools 6.12.0-211.67.1.el10_2, kernel-modules 6.12.0-211.67.1.el10_2, kernel-64k-core 6.12.0-211.67.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:85321
show 10 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-687.59.1.el9_8, kernel-debuginfo-common-s390x 5.14.0-687.59.1.el9_8, kernel-debuginfo-common-x86_64 5.14.0-687.59.1.el9_8, kernel-debuginfo-common-aarch64 5.14.0-687.59.1.el9_8, kernel-debuginfo-common-ppc64le 5.14.0-687.59.1.el9_8
    fixed: vendor fix RHSA-2026:86033
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.67.1.el10_2
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.176.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.176.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.176.1.el8_10
    fixed: vendor fix RHSA-2026:85773
  • Red Hat Enterprise Linux Hidden (v. 10) kernel-modules-internal 6.12.0-211.67.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.67.1.el10_2
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-kvm 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-kvm 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-core 4.18.0-553.176.1.rt7.517.el8_10, +4 more
    fixed: vendor fix RHSA-2026:85774
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-687.59.1.el9_8, kernel-rt-64k 5.14.0-687.59.1.el9_8, kernel-rt-core 5.14.0-687.59.1.el9_8, kernel-rt-modules 5.14.0-687.59.1.el9_8, kernel-rt-64k-core 5.14.0-687.59.1.el9_8, kernel-rt-debug-core 5.14.0-687.59.1.el9_8, +14 more
    fixed: vendor fix RHSA-2026:86033
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-211.67.1.el10_2, kernel-rt-64k 6.12.0-211.67.1.el10_2, kernel-rt-core 6.12.0-211.67.1.el10_2, kernel-rt-modules 6.12.0-211.67.1.el10_2, kernel-rt-64k-core 6.12.0-211.67.1.el10_2, kernel-rt-debug-core 6.12.0-211.67.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-687.59.1.el9_8, kernel-rt-core 5.14.0-687.59.1.el9_8, kernel-rt-modules 5.14.0-687.59.1.el9_8, kernel-rt-debug-core 5.14.0-687.59.1.el9_8, kernel-rt-modules-core 5.14.0-687.59.1.el9_8, kernel-rt-debug-modules 5.14.0-687.59.1.el9_8, +4 more
    fixed: vendor fix RHSA-2026:86033
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-211.67.1.el10_2, kernel-rt-core 6.12.0-211.67.1.el10_2, kernel-rt-modules 6.12.0-211.67.1.el10_2, kernel-rt-debug-core 6.12.0-211.67.1.el10_2, kernel-rt-modules-core 6.12.0-211.67.1.el10_2, kernel-rt-debug-modules 6.12.0-211.67.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:85321
  • Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-core 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-debug-modules 4.18.0-553.176.1.rt7.517.el8_10, kernel-rt-modules-extra 4.18.0-553.176.1.rt7.517.el8_10, +2 more
    fixed: vendor fix RHSA-2026:85774

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

0.14% chance of exploitation in the next 30 days, higher than 3% 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
  • CWE-191 Integer Underflow (Wrap or Wraparound)
  • CWE-787 Out-of-bounds Write
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.