CVE-2026-64009
xfrm: Check for underflow in xfrm_state_mtu
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.
INFO
Published Date :
July 19, 2026, 4:17 p.m.
Last Modified :
July 30, 2026, 2:59 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 |
Solution
- Apply kernel patch to fix xfrm_state_mtu underflow.
- Check for underflow in xfrm_state_mtu.
- Return error code on underflow detection.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-64009.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-64009 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-64009
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-64009 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-64009 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 20, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 19, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '8014f70c4e6e5ab101ae3860a614e65e988372e3', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '1021d2877b689a648b27815c854557a917122e93', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '2a41b1b31c61c52b972278ce1732a1443f5e89ed', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': 'fccd685b32df5aaf6bad4381eeda216468e283f0', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '820e501be8aee4b365d218d83227b314309c5fda', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '82ac903e0b519849647657b8c48d21237ada06a2', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '3db50ceeacb52806d8fe86fb1dfe944df0b9f789', 'versionType': 'git'}, {'status': 'affected', 'version': 'c5c2523893747f88a83376abad310c8ad13f7197', 'lessThan': '742b04d0550b0ec89dcbc99537ec88653bd1ad90', 'versionType': 'git'}], 'programFiles': ['net/xfrm/xfrm_state.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '2.6.22'}, {'status': 'unaffected', 'version': '0', 'lessThan': '2.6.22', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '5.10.259', 'versionType': 'semver', 'lessThanOrEqual': '5.10.*'}, {'status': 'unaffected', 'version': '5.15.210', 'versionType': 'semver', 'lessThanOrEqual': '5.15.*'}, {'status': 'unaffected', 'version': '6.1.176', 'versionType': 'semver', 'lessThanOrEqual': '6.1.*'}, {'status': 'unaffected', 'version': '6.6.143', 'versionType': 'semver', 'lessThanOrEqual': '6.6.*'}, {'status': 'unaffected', 'version': '6.12.93', 'versionType': 'semver', 'lessThanOrEqual': '6.12.*'}, {'status': 'unaffected', 'version': '6.18.35', 'versionType': 'semver', 'lessThanOrEqual': '6.18.*'}, {'status': 'unaffected', 'version': '7.0.12', 'versionType': 'semver', 'lessThanOrEqual': '7.0.*'}, {'status': 'unaffected', 'version': '7.1', 'versionType': 'original_commit_for_fix', 'lessThanOrEqual': '*'}], 'programFiles': ['net/xfrm/xfrm_state.c'], 'defaultStatus': 'affected'}] Added 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. Added Reference https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93 Added Reference https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed Added Reference https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789 Added Reference https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90 Added Reference https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3 Added Reference https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda Added Reference https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2 Added Reference https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0