CVE-2026-64009

System crash via ESP MTU arithmetic underflow

Published Jul 19, 2026 · Updated Jul 19, 2026

Out-of-bounds write in affected Linux Kernel branches starting at 2.6.22 allows local users to crash the system through an IPv4 ESP tunnel. xfrm_state_mtu subtracts attacker-controlled ESP overhead from a small MTU in unsigned arithmetic; esp_output then sign-extends the negative padding length into a massive memset size. Exploitation requires control of an XFRM security association, interface MTU, and TFC padding through CAP_NET_ADMIN, which a local user can obtain in a user namespace; the demonstrated result is kernel memory corruption and a system crash.

CVSS severity7.8
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in affected Linux Kernel branches starting at 2.6.22 allows local users to crash the system through an IPv4 ESP tunnel. xfrm_state_mtu subtracts attacker-controlled ESP overhead from a small MTU in unsigned arithmetic; esp_output then sign-extends the negative padding length into a massive memset size. Exploitation requires control of an XFRM security association, interface MTU, and TFC padding through CAP_NET_ADMIN, which a local user can obtain in a user namespace; the demonstrated result is kernel memory corruption and a system crash.

The record

CVE
CVE-2026-64009
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-787, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.6.22
  2. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <1021d2877b689a648b27815c854557a917122e93
  3. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <2a41b1b31c61c52b972278ce1732a1443f5e89ed
  4. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <3db50ceeacb52806d8fe86fb1dfe944df0b9f789
  5. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <742b04d0550b0ec89dcbc99537ec88653bd1ad90
  6. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <8014f70c4e6e5ab101ae3860a614e65e988372e3
  7. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <820e501be8aee4b365d218d83227b314309c5fda
  8. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <82ac903e0b519849647657b8c48d21237ada06a2
  9. Affected versionversion=c5c2523893747f88a83376abad310c8ad13f7197 <fccd685b32df5aaf6bad4381eeda216468e283f0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=2.6.22; version=c5c2523893747f88a83376abad310c8ad13f7197 <1021d2877b689a648b27815c854557a917122e93; version=c5c2523893747f88a83376abad310c8ad13f7197 <2a41b1b31c61c52b972278ce1732a1443f5e89ed; version=c5c2523893747f88a83376abad310c8ad13f7197 <3db50ceeacb52806d8fe86fb1dfe944df0b9f789; version=c5c2523893747f88a83376abad310c8ad13f7197 <742b04d0550b0ec89dcbc99537ec88653bd1ad90; version=c5c2523893747f88a83376abad310c8ad13f7197 <8014f70c4e6e5ab101ae3860a614e65e988372e3; version=c5c2523893747f88a83376abad310c8ad13f7197 <820e501be8aee4b365d218d83227b314309c5fda; version=c5c2523893747f88a83376abad310c8ad13f7197 <82ac903e0b519849647657b8c48d21237ada06a2; version=c5c2523893747f88a83376abad310c8ad13f7197 <fccd685b32df5aaf6bad4381eeda216468e283f0

Published CVSS scores

7.0Red HatCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8kernel.orgCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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