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# Linux Kernel vulnerability analysis and mitigation

<table data-header-hidden><thead><tr><th width="229"></th><th></th></tr></thead><tbody><tr><td>CVE:</td><td>CVE-2025-21759</td></tr><tr><td>Publication Date:</td><td>2024-Dec-29</td></tr><tr><td>Severity:</td><td>N/A</td></tr><tr><td>Reference:</td><td><a href="https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-21759">CVE-2025-21759</a><a href="https://papers.mathyvanhoef.com/usenix2021.pdf 
">
</a></td></tr><tr><td>Status:</td><td>Fixed</td></tr></tbody></table>

## Overview

CVE-2025-21759 affects the Linux kernel's IPv6 multicast functionality. The vulnerability was discovered in February 2025 and involves a potential Use-After-Free (UAF) issue in the igmp6*send() function. The vulnerability occurs because igmp6*send() can be called without RTNL or RCU being held, which could lead to unsafe network pointer fetching ([Kernel Git](https://git.kernel.org/stable/c/087c1faa594fa07a66933d750c0b2610aa1a2946)).

## Technical details

The vulnerability exists in the igmp6*send() function within the IPv6 multicast implementation. The issue stems from insufficient RCU (Read-Copy-Update) protection when accessing network namespace pointers. The function previously used sock*alloc*send*skb() which was problematic because ipv6.igmp*sk uses GFP*KERNEL allocations that can sleep. The fix involves extending RCU protection and using alloc*skb() instead, while charging the net->ipv6.igmp*sk socket under RCU protection ([Kernel Git](https://git.kernel.org/stable/c/087c1faa594fa07a66933d750c0b2610aa1a2946)). The vulnerability has been assigned a CVSS v3.1 score of 5.5 (Medium) ([Snyk](https://snyk.io/vuln/SNYK-CENTOS7-KERNELHEADERS-9033110)).

## Impact

The vulnerability could lead to a Use-After-Free condition when handling IPv6 multicast operations. This could potentially result in system crashes or memory corruption. The primary impact is on system availability, with a potential for complete loss of availability while the attack is ongoing ([Snyk](https://snyk.io/vuln/SNYK-CENTOS7-KERNELHEADERS-9033110)).

## Mitigation and workarounds

Upgrade ECS10xx/11xx/12xx/25xx to v1.2.115 to fix thisvulnerability.

Upgrade ECS55xx to v2.2.45 to fix this vulnerability.


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