CVE-2026-63921

Cross-tenant IPsec traffic hijacking via namespace mismatch

Published Jul 19, 2026 · Updated Jul 19, 2026

Improper network-namespace isolation in affected Linux Kernel releases allows local users to hijack another tenant's VTI6 traffic. vti6_siocdevprivate() looks up a migrated tunnel in dev_net(dev) but vti6_update() inserts it into t->net, poisoning the creation namespace's hash bucket. An unprivileged user namespace and CAP_NET_ADMIN only in the migrated namespace suffice to intercept, alter, or drop matched IPsec traffic on container hosts.

CVSS severity8.8
High
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper network-namespace isolation in affected Linux Kernel releases allows local users to hijack another tenant's VTI6 traffic. vti6_siocdevprivate() looks up a migrated tunnel in dev_net(dev) but vti6_update() inserts it into t->net, poisoning the creation namespace's hash bucket. An unprivileged user namespace and CAP_NET_ADMIN only in the migrated namespace suffice to intercept, alter, or drop matched IPsec traffic on container hosts.

The record

CVE
CVE-2026-63921
Published
Jul 19, 2026
Updated
Jul 19, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-653, T1565.002, T1040
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=3.15
  2. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <1acfb7d9c6fc7e209ed7789392697e97e03edd33
  3. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <44d2ff7d2178503b93151140a45dfa2ad49c9906
  4. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <596f6354c96a891e58c04a09cbfb7b0d1ec00dab
  5. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <853f6ea482dfcd3404bbef458ab4d68364eed838
  6. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <8b484efd5cb4eeef9021a661e198edc5349dacf6
  7. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <94ff740a7f9ef5c010784a325dca00cbf228f941
  8. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <d2236348414bdd6558385f35aa7fdc9bf5634011
  9. Affected versionversion=61220ab349485d911083d0b7990ccd3db6c63297 <df42ac708acc3399bbb6dc5ca16e0540adda7bbf

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=3.15; version=61220ab349485d911083d0b7990ccd3db6c63297 <1acfb7d9c6fc7e209ed7789392697e97e03edd33; version=61220ab349485d911083d0b7990ccd3db6c63297 <44d2ff7d2178503b93151140a45dfa2ad49c9906; version=61220ab349485d911083d0b7990ccd3db6c63297 <596f6354c96a891e58c04a09cbfb7b0d1ec00dab; version=61220ab349485d911083d0b7990ccd3db6c63297 <853f6ea482dfcd3404bbef458ab4d68364eed838; version=61220ab349485d911083d0b7990ccd3db6c63297 <8b484efd5cb4eeef9021a661e198edc5349dacf6; version=61220ab349485d911083d0b7990ccd3db6c63297 <94ff740a7f9ef5c010784a325dca00cbf228f941; version=61220ab349485d911083d0b7990ccd3db6c63297 <d2236348414bdd6558385f35aa7fdc9bf5634011; version=61220ab349485d911083d0b7990ccd3db6c63297 <df42ac708acc3399bbb6dc5ca16e0540adda7bbf

Published CVSS scores

8.8Linux kernel CNACVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
7.0Red HatCVSS:3.1/AV:L/AC:H/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-653Improper Isolation or Compartmentalization
T1565.002Transmitted Data Manipulation
T1040Network Sniffing

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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