High

Linux kernel IPv6 ip6_output() use-after-free

IdentifiersCVE-2025-40158CWE-416

CVE-2025-40158 is a Linux kernel vulnerability in the IPv6 networking stack. The issue is associated with the ip6_output() path, where missing or insufficient RCU protection around destination-device access could permit a possible use-after-free condition. The fix changes ip6_output() to use RCU so that dst_dev_rcu() can be used safely, and correspondingly removes now-redundant rcu_read_lock()/rcu_read_unlock() pairs from ip6_finish_output2(). The flaw affects kernel memory lifetime handling in the IPv6 output path and can expose the kernel to unsafe access to freed objects during packet processing.

For your environment

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation could trigger kernel memory safety violations in the IPv6 transmit path, leading to kernel crashes, system instability, or denial of service. Because the flaw is a possible use-after-free in kernel networking code, memory corruption effects may also create conditions for integrity impact or further exploitation, although the available information does not confirm reliable code execution.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by limiting access to local untrusted users and minimizing the ability to exercise affected IPv6 networking paths. Where operationally feasible, restrict or disable unnecessary IPv6 functionality until patched kernels can be deployed. Mitigation is only partial; installing a fixed kernel is the definitive solution.

Remediation

Patch, then assume compromise.

Update to a Linux kernel release that includes the fix for CVE-2025-40158, specifically the change to use RCU in ip6_output() and safe destination-device access via dst_dev_rcu(). Apply the relevant vendor kernel security updates for affected distributions and reboot the system after installation so the patched kernel is loaded.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

LinuxLinux Kerneloperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

20 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

20 SOURCESView more in app

redhat accessNews

Jun 22, 2026

RHSA-2026:27731 - Security Advisory - Red Hat Customer Portal

A Linux kernel IPv6 flaw in ip6_output() addressed by using RCU.

redhat accessNews

Jun 17, 2026

RHSA-2026:26515 - Security Advisory - Red Hat Customer Portal

Linux kernel IPv6 vulnerability related to use of RCU in ip6_output().

redhat accessNews

Jun 17, 2026

RHSA-2026:26462 - Security Advisory - Red Hat Customer Portal

Linux kernel IPv6 vulnerability related to use of RCU in ip6_output().

redhat accessNews

Jun 17, 2026

RHSA-2026:26535 - Security Advisory - Red Hat Customer Portal

A Linux kernel IPv6 vulnerability in ip6_output() fixed by using RCU.

+8 more in the timeline

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1