What is CVE-2026-98432?

CVE-2026-98432 is a critical Use-After-Free (UAF) race condition in the Linux kernel's IPv4 TCP handshake implementation (tcp_v4_syn_recv_sock) affecting kernel versions 4.4 and later. When TCP SYN packets containing IP options are received, ownership of ireq_opt options is transferred without reference duplication. Concurrent retransmissions or premature socket closures free this memory block while it is still referenced, allowing unauthenticated remote attackers to trigger kernel crashes or execute arbitrary code with root privileges.

Is HTTP/2 responsible for CVE-2026-98432?

No. CVE-2026-98432 is strictly an OS-level Linux kernel network stack flaw (Layer 4 TCP/IPv4), not an HTTP/2 protocol bug (Layer 7). Any open TCP port on a vulnerable Linux machine (including ports 80, 443, 22, 8080, or microservice ports) exposes the host to the handshake race condition, regardless of whether HTTP/1.1, HTTP/2, or plain TCP is running on top.

Why is Multipath TCP (MPTCP) highlighted in CVE-2026-98432 exploits?

MPTCP listener state machines alter how child sockets and connection states are created and destroyed. Security researchers demonstrated that hosts running MPTCP listeners—such as modern Go networking applications where MPTCP is enabled by default—provide reliable exploit timing to achieve remote root code execution.

How can I mitigate CVE-2026-98432 immediately?

1. Upgrade your Linux kernel to the latest distribution release containing upstream commit e3f33b0a1d89 and reboot. 2. Immediately disable MPTCP: run 'sudo sysctl -w net.mptcp.enabled=0' and add 'net.mptcp.enabled = 0' to /etc/sysctl.conf. 3. Configure perimeter firewalls to drop incoming IPv4 packets with IP options: 'iptables -A INPUT -p tcp -m ipv4options --any-opt -j DROP'.

CVE-2026-98432 Scanner - Linux Kernel TCP UAF & RCE Detection

Name: Bspeka CVE-2026-98432 Linux TCP Vulnerability Scanner
Brand: Bspeka
Rating: 5.0 (1 reviews)

Technical Breakdown of CVE-2026-98432

How a memory management race condition in the Linux TCP connection handshake allows unauthenticated remote exploitation.

The Handshake Handover Race Condition

When an incoming IPv4 TCP SYN packet contains IP options, the Linux kernel stores them in ireq_opt. Upon handshake completion in tcp_v4_syn_recv_sock, ownership is transferred directly to the child socket without duplicating references. A concurrent SYN retransmit or rapid connection teardown causes a double-dereference and Use-After-Free condition.

Why It Affects Any TCP Port (Not Just HTTP/2)

Because the vulnerability lives inside the kernel's Layer 4 TCP/IP implementation (net/ipv4/tcp_ipv4.c), it executes before any Layer 7 application protocol is parsed. Web servers, SSH daemons, databases, or custom microservices running on a vulnerable Linux kernel are equally reachable.

The Role of MPTCP in Exploit Reliability

Security research demonstrated that hosts with Multipath TCP (MPTCP) listeners—which is enabled by default in many modern language runtimes such as Go—exhibit socket memory reuse timing that enables reliable unauthenticated remote root execution.

Distribution Patch Matrix & Scope

Cross-reference your cloud hosts and servers against affected Linux distributions.

Platform / Distribution	Vulnerable Kernel Scope	Patched Package / Upstream Fix	Impact
Ubuntu Linux (20.04, 22.04, 24.04 LTS)	Kernel ≥ 4.4 unpatched	USN-72xx Kernel Security Update	CRITICAL (CVSS 9.8)
RHEL / AlmaLinux / Rocky Linux (8, 9)	All unpatched kernel releases	RHSA-2026:xxxx Kernel Errata	CRITICAL (CVSS 9.8)
Amazon Linux (AL2, AL2023)	Unpatched AMI kernels	ALAS2026 Kernel Update	CRITICAL (CVSS 9.8)
Hosts with MPTCP Disabled (net.mptcp.enabled=0)	Exploit vector mitigated	Workaround active (RCU fix still advised)	REDUCED RISK

Frequently Asked Questions

Clarifying the nature, scope, and remediation of CVE-2026-98432.

Is CVE-2026-98432 an HTTP/2 vulnerability?

No. CVE-2026-98432 is an operating system kernel flaw in the Linux IPv4 TCP implementation. It occurs during the initial TCP 3-way handshake before any application-level protocol (such as HTTP/1.1 or HTTP/2) begins transmitting data. It was discussed alongside web services because internet-facing web servers and Go microservices represent the most accessible targets for attackers to send raw TCP handshake packets.

How does bspeka detect CVE-2026-98432 exposure?

bspeka maps your public domain perimeter to identify internet-facing TCP services, evaluates TCP/IP stack response characteristics to detect Linux kernels, inspects server banners, and tests for MPTCP indicators—all through safe, non-destructive network probes without sending exploit payloads.

What is the permanent upstream fix?

The upstream Linux kernel fix is commit e3f33b0a1d89 ("ipv4: free inet_opt and ireq_opt after an RCU grace period"), which ensures socket options are not deallocated until an RCU grace period has completed, preventing concurrent CPUs from accessing freed memory.

CVE-2026-98432 Linux TCP UAF & Remote Code Execution Scanner