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CVE-2026-43091 Linux CVE debrief

A use-after-free vulnerability exists in the Linux kernel's XFRM (IPsec transform) subsystem during network namespace teardown. The xfrm_policy_fini() function frees policy_bydst hash tables without waiting for concurrent RCU readers to exit their critical sections. Since these tables are published via rcu_assign_pointer() and accessed through rcu_dereference_check(), premature freeing allows use-after-free access by lingering RCU readers. The fix adds synchronize_rcu() before freeing the hash table memory to ensure all RCU readers have completed. This is a local privilege escalation vulnerability requiring low privileges and no user interaction.

Vendor
Linux
Product
Unknown
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-06
Original CVE updated
2026-05-19
Advisory published
2026-05-06
Advisory updated
2026-05-19

Who should care

System administrators running Linux kernels with IPsec/XFRM and network namespaces; container platform operators; VPN infrastructure teams; security teams tracking kernel privilege escalation vectors

Technical summary

The vulnerability is a use-after-free in net/xfrm/xfrm_policy.c during network namespace teardown. The policy_bydst hash tables are RCU-protected but xfrm_policy_fini() freed them without calling synchronize_rcu(), allowing concurrent RCU readers to access freed memory. The fix adds synchronize_rcu() before kfree(table) calls. Affected versions span 4.9 through 6.19.14 and 7.0-rc1 through 7.0-rc7. CVSS 3.1 score 7.8 (HIGH) with vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H indicates local attack vector with high impact on confidentiality, integrity, and availability.

Defensive priority

HIGH

Recommended defensive actions

  • Apply kernel patches from stable branches: 6.6.136+, 6.12.83+, 6.18.24+, 6.19.14+, or 7.0-rc8+ when available
  • If immediate patching is not possible, avoid frequent network namespace creation/destruction cycles that trigger xfrm_policy_fini()
  • Monitor for kernel updates from distribution vendors for backported fixes
  • Review systems using IPsec/XFRM with network namespaces (containers, VPNs) for abnormal behavior
  • Validate kernel version through uname -r and compare against fixed versions in CPE criteria

Evidence notes

The vulnerability description is sourced from the official CVE record published 2026-05-06 and modified 2026-05-19. The fix involves adding synchronize_rcu() to properly wait for RCU grace periods during xfrm policy netns exit. Multiple stable kernel patches have been released across affected branches.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-43091 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-43091

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-43091 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-43091

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/069daad4f2ae9c5c108131995529d5f02392c446

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/33a3149dd81a1e2f52b80ee1e0fc380b39f3d028

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/3733fce2871c9bca9dd18a1a23b1432ea215a094

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/438b1f668ad58f46ce699bb48e4698a7839e3f9e

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/b66920a3348c0f63ba18365248fa21fbf0b3a937

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.