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CVE-2026-64525· NVD / CVE Program· CNA Linux

xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit

In the Linux kernel, the following vulnerability has been resolved: xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit The struct pernet_operations docstring in include/net/net_namespace.h explicitly warns against blocking RCU primitives in .exit handlers: Exit methods using blocking RCU primitives, such as synchronize_rcu(), should be implemented via exit_batch. [...] Please, avoid synchronize_rcu() at all, where it's possible. Note that a combination of pre_exit() and exit() can be used, since a synchronize_rcu() is guaranteed between the calls. xfrm_policy_fini() violates this: it calls synchronize_rcu() before freeing the policy_bydst hash tables (so no RCU reader is mid- traversal at free time), but runs from xfrm_net_ops.exit -- once per namespace -- so a cleanup_net() of N namespaces pays N full RCU grace periods serially. Use the documented pre_exit/exit split. Move the policy flush (and the workqueue drains it depends on) into a new .pre_exit handler; xfrm_policy_fini() then runs in .exit and frees the hash tables after the synchronize_rcu_expedited() that cleanup_net() guarantees between the two phases. Providing O(1) RCU grace periods per batch instead of O(N). Observed on Linux 6.18 with a workload doing unshare(CLONE_NEWNET) at ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread both stuck in xfrm_policy_fini()'s synchronize_rcu(), >300k struct net accumulated in the cleanup queue, Percpu in /proc/meminfo climbed to 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and __put_net counts were balanced, ruling out a refcount leak.

—No exploit Fix available
Published
Jul 25, 2026
Updated
Jul 25, 2026
EPSS
0.2% · 10th percentile
CWE
—
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CVSS
0 / 40 · —
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

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Affected systems

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Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • b66920a3348c0f63ba18365248fa21fbf0b3a937, 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028, 7.0affected
    • 438b1f668ad58f46ce699bb48e4698a7839e3f9e and later · before bca6386dc08750fc7cdcbc7683473748ba3114b9affected · git
    • 3733fce2871c9bca9dd18a1a23b1432ea215a094 and later · before 91cc13978ab0bc6f669139f53e7e613a860d10e0affected · git
    • 069daad4f2ae9c5c108131995529d5f02392c446 and later · before d14ae8ef88c2c6590e107db61b6adce148cec7b3affected · git
    • 069daad4f2ae9c5c108131995529d5f02392c446 and later · before 3e52417318473782012b236d0325bf7d2266a597affected · git
    • 6.12.83 and later · before 6.12.93affected · semver
    • 6.18.24 and later · before 6.18.35affected · semver
    • 6.6.136 and later · before 6.7affected · semver
    • 6.19.14 and later · before 6.20affected · semver
    • before 7.0not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:13linuxbefore 6.12.94-16.12.94-1
Debian:14linuxbefore 7.0.12-17.0.12-1

Same product

linux: all records

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Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux3e52417318473782012b236d0325bf7d2266a597Vendor (CNA)
Linux Linux6.12.93Vendor (CNA)
Linux Linux6.18.35Vendor (CNA)
Linux Linux6.20Vendor (CNA)
Linux Linux6.7Vendor (CNA)
Linux Linux91cc13978ab0bc6f669139f53e7e613a860d10e0Vendor (CNA)
Linux Linuxbca6386dc08750fc7cdcbc7683473748ba3114b9Vendor (CNA)
Linux Linuxd14ae8ef88c2c6590e107db61b6adce148cec7b3Vendor (CNA)
azl3 kernel 6.6.152.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
azl3 kernel 6.6.157.1-1 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
debian:linux6.12.94-1 · Debian:13Package registry (OSV)

Exploit status

No known public exploit

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Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

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EPSS, last 120 days

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Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

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—

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References

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