{"id":10398,"date":"2026-11-11T17:36:19","date_gmt":"2026-11-11T17:36:19","guid":{"rendered":"https:\/\/cybersecurityinfocus.com\/?p=10398"},"modified":"2026-11-11T17:36:19","modified_gmt":"2026-11-11T17:36:19","slug":"linux-kernel-use-after-free-vulnerability-whats-happening-and-why-it-matters","status":"publish","type":"post","link":"https:\/\/cybersecurityinfocus.com\/?p=10398","title":{"rendered":"Linux Kernel Use-After-Free Vulnerability: What\u2019s Happening and Why It Matters"},"content":{"rendered":"
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Linux does a lot of work behind the scenes. It handles memory, manages network connections, runs applications, and keeps everything working together. We don\u2019t usually think about any of this because, well, it\u2019s supposed to just work.<\/p>\n

But what happens when something goes wrong?<\/p>\n

That\u2019s where CVE-2026-98432<\/a> \u2013 Linux Kernel IPv4 TCP Use-After-Free Vulnerability comes in.<\/p>\n

It\u2019s a critical flaw in the Linux kernel that lets attackers trigger a memory issue by sending specially crafted network packets. This could crash the system, corrupt memory, or even allow remote code execution.<\/p>\n

What\u2019s worse, attackers don\u2019t need to log in or trick anyone into clicking a link.<\/p>\n

So, what\u2019s actually going wrong? How can sending a few network packets cause so much trouble? What steps should organizations take to address this?<\/p>\n

Let\u2019s analyze it.<\/p>\n<\/div>\n<\/div>\n

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First, What’s Actually Going Wrong? <\/h2>\n<\/div>\n<\/div>\n
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CVE-2026-98432 is a use-after-free vulnerability, or UAF for short.<\/p>\n

Here\u2019s what it means.<\/p>\n

Think of memory as a space where programs temporarily keep the information they need. When they\u2019re done with that information, they release the space so it can be used for something else.<\/p>\n

That\u2019s perfectly normal.<\/p>\n

The problem occurs when a program tries to use that same memory after it has already been released. It shouldn\u2019t happen, but sometimes it does. This is known as a use-after-free vulnerability.<\/p>\n

Now, let\u2019s bring that back to Linux.<\/p>\n

The kernel manages socket options when it\u2019s handling incoming IPv4 TCP connections. With this vulnerability, it can release the memory holding those options while another operation is still trying to use them.<\/p>\n

That\u2019s the problem in a nutshell.<\/p>\n

CVE-2026-98432 has a CVSS v3.1 score of 9.8, which puts it in the Critical category. An attacker doesn\u2019t need to authenticate or have access to the system to try exploiting it. They can send specially crafted IPv4 TCP packets containing IP options to an affected system.<\/p>\n

There\u2019s another important detail here. Researchers demonstrated remote code execution<\/a> against systems with a Multipath TCP (MPTCP) listener.<\/p>\n

AWS also reported that it had no evidence of the vulnerability being exploited in the wild at the time of its advisory.<\/p>\n

But how does the kernel end up releasing memory that\u2019s still being used?<\/p>\n<\/div>\n<\/div>\n

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A Terrain-Based, Risk-Informed Approach to Track Key Vulnerabilities<\/div>\n<\/div>\n<\/div>\n
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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tTrack Key Vulnerabilities and Exposures (CVEs)<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tVisibility to Risk: Prioritizing CVEs<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tTerrain-Aware Defense<\/span><\/p><\/div>\n<\/div>\n

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\n\t\t\t\t\t\t\t\t\tDownload Whitepaper<\/span>
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So, How Does the Vulnerability Work?<\/h2>\n<\/div>\n<\/div>\n
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Let\u2019s start with something familiar:<\/strong> a device trying to connect to a Linux server.<\/p>\n

When that connection request reaches the server, the Linux kernel has to process it and keep track of the information needed to establish the connection. Some of that information is stored in socket options.<\/p>\n

Normally, this process should happen without any problems.<\/p>\n

However, in this instance, the kernel moves those socket settings to a newly created child socket from a request socket. Instead of creating a separate copy, it transfers ownership of the existing memory.<\/p>\n

Another operation might still be using those same socket options. For example, one CPU could be handling a new connection while another is processing a retransmitted SYN request for that connection.<\/p>\n

Now imagine the child socket gets freed while that second operation is still running.<\/p>\n

The memory is gone, but the other operation hasn\u2019t finished using it. When it tries to access that memory again, the kernel runs into a use-after-free condition.<\/p>\n

Here\u2019s the sequence in simpler terms:<\/p>\n<\/div>\n<\/div>\n

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tAn attacker sends specially crafted IPv4 TCP packets to a system that’s listening for connections.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tThe kernel processes the connection and transfers the socket options to a child socket.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tAt the same time, another CPU may be handling a retransmitted SYN request and trying to access those same options.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tThe child socket gets freed before the other operation finishes. <\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tThe second operation tries to access the memory even though it has already been released.<\/span><\/p><\/div>\n<\/div>\n

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And that\u2019s how the problem occurs.<\/p>\n

This is what\u2019s known as a race condition. Two operations are happening at the same time, and the kernel isn\u2019t handling the memory release safely.<\/p>\n

There\u2019s another way to run into a similar problem, too.<\/p>\n

It\u2019s called request socket migration. Basically, the kernel moves a connection request from one socket to another. During this process, the original and cloned request sockets can share the same socket options.<\/p>\n

That creates another opportunity for one operation to release the memory while another is still using it.<\/p>\n

So, the real issue here is timing. The kernel needs to wait until other operations are finished using the memory before releasing it. In this case, it doesn\u2019t always do that.<\/p>\n<\/div>\n<\/div>\n

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What Can Actually Happen If Someone Exploits It?<\/h2>\n<\/div>\n<\/div>\n
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Okay, so we know what\u2019s going wrong inside the kernel. But what does this mean for an organization running Linux systems?<\/p>\n

Unfortunately, the impact can be quite serious.<\/p>\n

Depending on the conditions, an attacker could potentially trigger:<\/p>\n<\/div>\n<\/div>\n

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\n\t\t\t\t\t\t\t\t\t\tSystem crashes: If the kernel tries to access invalid memory, it could crash the system and interrupt the services running on it.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tMemory corruption: The kernel could end up accessing memory that’s already been released, potentially affecting other operations.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tMemory disclosure: Under certain conditions, information stored in kernel memory could be exposed.<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tRemote code execution: Researchers demonstrated unauthenticated remote code execution against systems with an MPTCP listener.<\/span><\/p><\/div>\n<\/div>\n

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The remote attack aspect is particularly important.<\/p>\n

An attacker doesn\u2019t need an account, special permissions, or someone to interact with a malicious file or link. They can attempt to trigger the vulnerable code remotely by sending specially crafted network packets.<\/p>\n

For organizations running Linux servers that accept incoming TCP connections, that\u2019s definitely something to pay attention to.<\/p>\n<\/div>\n<\/div>\n

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How Do You Know If Your Linux Systems Are Affected?<\/h2>\n<\/div>\n<\/div>\n
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If you\u2019re responsible for a Linux environment, this is probably the next thing on your mind.<\/p>\n

CVE-2026-98432 affects Linux kernel versions 4.4 and later. But that doesn\u2019t automatically mean every system running one of these versions is vulnerable.<\/p>\n

Additionally, it depends on the Linux distribution, the kernel branch, and whether or not the necessary security patches have been installed.<\/p>\n

Several vendors, including Amazon Linux, Red Hat, SUSE, and Debian, have published advisories and fixes.<\/p>\n

Here\u2019s something else to watch out for: Linux distributions often backport security fixes to older kernel versions.<\/p>\n

In other words, a system might already have the fix even if its kernel version looks older. So, don\u2019t rely on the version number alone when checking for vulnerable systems.<\/p>\n

If you\u2019re reviewing your environment, start with these questions:<\/strong><\/em><\/p>\n<\/div>\n<\/div>\n

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\n\t\t\t\t\t\t\t\t\t\tAre any of your Linux servers running potentially affected kernel builds?<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tHave you installed the security updates recommended by your Linux distribution?<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tAre these systems accepting incoming IPv4 TCP connections?<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tAre you using Multipath TCP or request socket migration?<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\t\tHave you rebooted the affected systems after installing the kernel update?<\/span><\/p><\/div>\n<\/div>\n

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And don\u2019t stop with your physical servers. Check your cloud-based Linux instances, too. They can easily get overlooked when organizations are reviewing their infrastructure.<\/p>\n<\/div>\n<\/div>\n

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How Can It Be Fixed?<\/h2>\n<\/div>\n<\/div>\n
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Now for the important part: fixing the issue.<\/p>\n

The good news is that vendors have released security updates. So, if you have an affected system, getting the fixed kernel installed should be your first step.<\/p>\n

The upstream fix changes how the kernel releases socket options. It uses kfree_rcu() to make sure memory isn\u2019t released until active readers have finished accessing it.<\/p>\n

So, what should you do next?<\/strong><\/em><\/p>\n<\/div>\n<\/div>\n

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1. Install the available kernel update <\/h3>\n<\/div>\n<\/div>\n
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First, check the security advisory<\/a> for your Linux distribution.<\/p>\n

Find the fixed kernel package recommended for your version and install it. The package you need may differ depending on the distribution and release you\u2019re running, so follow the vendor\u2019s instructions.<\/p>\n<\/div>\n<\/div>\n

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2. Reboot the affected systems<\/h3>\n<\/div>\n<\/div>\n
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Don\u2019t skip this step.<\/p>\n

Installing a kernel update doesn\u2019t necessarily mean your system is already running the updated kernel. You need to make sure the new kernel has actually been loaded.<\/p>\n

AWS specifically notes that affected self-managed EC2 instances must be rebooted after installing the update.<\/p>\n<\/div>\n<\/div>\n

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3. Can’t patch everything immediately? Use temporary mitigations<\/h3>\n<\/div>\n<\/div>\n
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We know that updating every system in a large environment isn\u2019t always something you can do overnight.<\/p>\n

If you need more time to roll out the patches, AWS recommends a few temporary measures to reduce exposure.<\/p>\n

For example, you can disable Multipath TCP using net.mptcp.enabled=0. Applications built with Go 1.24 or later can also use GODEBUG=multipathtcp=0 to disable MPTCP support.<\/p>\n

Another option is to block incoming IPv4 packets containing IP options using firewall rules. AWS provides an iptables rule for this, along with guidance for configuring AWS Network Firewall.<\/p>\n

Just remember that these measures are workarounds, not permanent fixes. They can help reduce exposure while you\u2019re working on the updates, but they don\u2019t address the underlying vulnerability.<\/p>\n<\/div>\n<\/div>\n

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4. Double-check that everything is updated <\/h3>\n<\/div>\n<\/div>\n
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Once the updates are installed and the systems have been rebooted, check that they\u2019re actually running the fixed kernel.<\/p>\n

It\u2019s also worth keeping a simple record of which systems have been updated, which kernel packages they\u2019re running, and when they were last rebooted.<\/p>\n

This helps you avoid missing systems during the patching process.<\/p>\n<\/div>\n<\/div>\n

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Is Patching Enough? What About Network Monitoring?<\/h2>\n<\/div>\n<\/div>\n
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Getting the security updates installed should obviously come first. But there\u2019s another thing organizations need to think about.<\/p>\n

What about the time between discovering the vulnerability and getting every affected system patched?<\/p>\n

You still need to know what\u2019s happening across your network during that period.<\/p>\n

Since CVE-2026-98432 involves incoming IPv4 TCP traffic, monitoring network activity can help security teams spot unusual patterns<\/a> and investigate anything that looks suspicious.<\/p>\n

For example, repeated SYN retransmissions, sudden bursts of TCP connection requests, or unexpected IPv4 packets containing IP options might be worth investigating.<\/p>\n

To be clear, these aren\u2019t confirmed signs of an attempt to exploit CVE-2026-98432. But they can give security teams additional context when looking into unusual network activity.<\/p>\n

This is where network detection and response (NDR) comes in.<\/p>\n

Fidelis Network<\/a>\u00ae uses Deep Session Inspection<\/a>\u00ae (DSI) to inspect traffic across ports and protocols. This helps security teams get a closer look at network communications, examine traffic details, and investigate suspicious activity.<\/p>\n

It also offers capabilities such as Network DLP<\/a>, sandboxing, and threat intelligence. These can help teams examine suspicious files and communications, investigate potential data movement, and understand what\u2019s happening across their network.<\/p>\n

Of course, network monitoring won\u2019t fix the kernel vulnerability. It doesn\u2019t replace patching, either.<\/p>\n

But it gives security teams another way to keep an eye on their environment, investigate unusual activity, and get a better understanding of what\u2019s happening while potentially vulnerable systems are still being updated.<\/p>\n<\/div>\n<\/div>\n

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Fidelis DSI – Advanced Data inspection and Threat Detection Capabilities<\/div>\n<\/div>\n<\/div>\n
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\n\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>
\n\t\t\t\t\t\t\t\t\t\tContent Inspection<\/span><\/p>\n

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\n\t\t\t\t\t\t\t\t\tDownload the Datasheet<\/span>
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\n\t\t\t\t\t<\/a>\n\t\t\t\t<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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So, What Should You Take Away from This?<\/h2>\n<\/div>\n<\/div>\n
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CVE-2026-98432 is a good example of how something as basic as memory management can turn into a serious security problem.<\/p>\n

The Linux kernel can end up accessing memory that\u2019s already been released because two operations are trying to use the same socket options at the same time. Additionally, this may result in system crashes, memory corruption, or even remote code execution, depending on the situation.<\/p>\n

Don\u2019t wait to find out if you are impacted if your company uses Linux.<\/p>\n

Review your systems, install the recommended kernel updates, and reboot where required. If you need more time to patch everything, look at the temporary mitigations recommended by your Linux vendor.<\/p>\n

And while you\u2019re doing all that, keep an eye on your network, too. Knowing what\u2019s happening across your environment can help security teams spot unusual activity and investigate potential threats before they turn into bigger problems.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

The post Linux Kernel Use-After-Free Vulnerability: What\u2019s Happening and Why It Matters<\/a> appeared first on Fidelis Security<\/a>.<\/p>","protected":false},"excerpt":{"rendered":"

Linux does a lot of work behind the scenes. It handles memory, manages network connections, runs applications, and keeps everything working together. We don\u2019t usually think about any of this because, well, it\u2019s supposed to just work. But what happens when something goes wrong? That\u2019s where CVE-2026-98432 \u2013 Linux Kernel IPv4 TCP Use-After-Free Vulnerability comes […]<\/p>\n","protected":false},"author":0,"featured_media":10399,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-10398","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news"],"_links":{"self":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts\/10398"}],"collection":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=10398"}],"version-history":[{"count":0,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts\/10398\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/media\/10399"}],"wp:attachment":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10398"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10398"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10398"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}