CyberSecBulletin
CVE-2026-64009NVD status: Modified

Linux: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-64009 is a high-severity out-of-bounds write vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 8014f70c4e6e5ab101ae3860a614e65e988372e3, 1021d2877b689a648b27815c854557a917122e93, 2a41b1b31c61c52b972278ce1732a1443f5e89ed as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.14% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 8014f70c4e6e5ab101ae3860a614e65e988372e3 or 1021d2877b689a648b27815c854557a917122e93 or 2a41b1b31c61c52b972278ce1732a1443f5e89ed or fccd685b32df5aaf6bad4381eeda216468e283f0, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.259 or 5.15.210 or 6.1.176 or 6.6.143, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxc5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 8014f70c4e6e5ab101ae3860a614e65e988372e3; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 1021d2877b689a648b27815c854557a917122e93; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 2a41b1b31c61c52b972278ce1732a1443f5e89ed; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, fccd685b32df5aaf6bad4381eeda216468e283f0; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 820e501be8aee4b365d218d83227b314309c5fda; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 82ac903e0b519849647657b8c48d21237ada06a2; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 3db50ceeacb52806d8fe86fb1dfe944df0b9f789; c5c2523893747f88a83376abad310c8ad13f7197 up to, but not including, 742b04d0550b0ec89dcbc99537ec88653bd1ad90; and 1 more ranges8014f70c4e6e5ab101ae3860a614e65e988372e3, 1021d2877b689a648b27815c854557a917122e93, 2a41b1b31c61c52b972278ce1732a1443f5e89ed, fccd685b32df5aaf6bad4381eeda216468e283f0, 820e501be8aee4b365d218d83227b314309c5fda, 82ac903e0b519849647657b8c48d21237ada06a2
LinuxLinux Kernel2.6.22 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.15.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, 6.18.35

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official description

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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Write vulnerabilities

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