VulnerabilityPublished 27 Jul 2026Updated 29 Oct 2026

CVE-2026-64525: Linux kernel · xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit

Affects Linux kernelSource GCVE Database

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Not known to be exploited · fixed in 6.8.0-1066.69~22.04.1 : update Linux kernel when convenient.

Data as of 30 Oct 2026, 05:36 UTC

Severity

Medium

Rated by Threat Radar · No CVSS score from NVD or the CNA

Patch: Available – fixed in 6.8.0-1066.69~22.04.1, 6.8.0-1070.78~22.04.1, 6.8.0-1068.75~22.04.1 +37

Exploitation evidence

Disclosed: evidence found.
CVE published 27 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Patches and advisories

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTSlinux`pkg:deb/ubuntu/linux?arch=source&distro=resolute`Other threats	Affected <7.0.0-28.28	Fixed in 7.0.0-28.28
Ubuntu 26.04 LTSlinux-aws`pkg:deb/ubuntu/linux-aws?arch=source&distro=resolute`Other threats	Affected <7.0.0-1009.9	Fixed in 7.0.0-1009.9
Ubuntu 26.04 LTSlinux-azure`pkg:deb/ubuntu/linux-azure?arch=source&distro=resolute`Other threats	Affected <7.0.0-1010.10	Fixed in 7.0.0-1010.10
Ubuntu 26.04 LTSlinux-azure-fde`pkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resolute`Other threats	Affected <7.0.0-1009.9	Fixed in 7.0.0-1009.9
Ubuntu 26.04 LTSlinux-gcp`pkg:deb/ubuntu/linux-gcp?arch=source&distro=resolute`Other threats	Affected <7.0.0-1008.8	Fixed in 7.0.0-1008.8
Ubuntu 26.04 LTSlinux-gke`pkg:deb/ubuntu/linux-gke?arch=source&distro=resolute`Other threats	Affected <7.0.0-1003.4	Fixed in 7.0.0-1003.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available and included in Linux kernel versions 6.8.0 and later for the affected distributions. Users should update to these fixed versions to resolve the issue. No additional mitigation is required as the fix addresses the root cause by properly splitting the cleanup phases into .pre_exit and .exit handlers.

Description

A Linux kernel vulnerability involving improper handling of RCU synchronization in the xfrm network policy cleanup process was fixed by moving the policy_bydst RCU sync from the per-netns .exit handler to the .pre_exit handler. This change prevents excessive blocking during namespace cleanup, which previously caused high memory usage and system instability under heavy network namespace creation workloads.

Impact

The vulnerability causes excessive blocking during network namespace cleanup, leading to accumulation of network namespace structures in the cleanup queue and very high memory consumption, which can trigger out-of-memory (OOM) conditions on large systems with many CPUs. This can degrade system stability and performance under workloads that create and destroy network namespaces rapidly. There is no indication of direct privilege escalation or code execution impact.

Summary

The vulnerability in the Linux kernel's xfrm subsystem was due to the use of synchronize_rcu() in the per-netns .exit handler (xfrm_net_ops.exit) during policy cleanup, which violated documented kernel guidelines against blocking RCU primitives in .exit handlers. This caused cleanup_net() to pay N full RCU grace periods serially when cleaning up N namespaces, leading to excessive blocking, accumulation of struct net objects in the cleanup queue, and very high memory usage (over 130 GB on 256-CPU hosts), resulting in out-of-memory conditions. The fix moves the policy flush and dependent workqueue drains into a new .pre_exit handler, ensuring O(1) RCU grace periods per batch and freeing the hash tables after an expedited synchronize_rcu() in .exit, improving cleanup efficiency and preventing resource exhaustion. The issue was observed on Linux kernel 6.18 and affects multiple older kernel versions.

References

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