CVE-2026-23242: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23242 Overview

CVE-2026-23242 is a NULL pointer dereference vulnerability in the Linux kernel's RDMA Software iWARP (siw) driver. The vulnerability exists in the TCP receive data path within the siw_tcp_rx_data() function. When siw_get_hdr() returns -EINVAL before set_rx_fpdu_context() is called, the qp->rx_fpdu pointer can remain NULL. The error path subsequently dereferences qp->rx_fpdu->more_ddp_segs without validating that rx_fpdu is non-NULL, leading to a kernel NULL pointer dereference.

Critical Impact

This vulnerability can cause kernel crashes and system instability when processing malformed RDMA over TCP packets, potentially leading to denial of service conditions on systems utilizing the siw driver for RDMA over Ethernet functionality.

Affected Products

• Linux kernel with RDMA/siw driver enabled
• Systems utilizing Software iWARP (siw) for RDMA over TCP/IP
• Multiple stable kernel branches (see patch references)

Discovery Timeline

• 2026-03-18 - CVE CVE-2026-23242 published to NVD
• 2026-03-18 - Last updated in NVD database

Technical Details for CVE-2026-23242

Vulnerability Analysis

The vulnerability occurs in the RDMA Software iWARP (siw) driver's TCP receive data processing logic. The siw driver implements the iWARP protocol over standard TCP/IP networking, enabling RDMA functionality without specialized hardware. During packet processing, the siw_get_hdr() function parses incoming header data. If this function encounters invalid header data and returns -EINVAL, the system transitions to an error handling path.

The flaw is that this error path assumes qp->rx_fpdu (the receive Frame Protocol Data Unit context) has been properly initialized by set_rx_fpdu_context(). However, when the error occurs early in processing, before context initialization, rx_fpdu remains NULL. The subsequent access to qp->rx_fpdu->more_ddp_segs triggers a NULL pointer dereference at offset 0xc0-0xc7 as identified by KASAN (Kernel Address Sanitizer).

Root Cause

The root cause is a missing NULL pointer check in the error handling path of siw_tcp_rx_data(). The code unconditionally accesses qp->rx_fpdu->more_ddp_segs without first verifying that rx_fpdu is non-NULL. This violates defensive programming practices where pointer validity should be confirmed before dereferencing, particularly in error handling paths where data structures may be in incomplete states.

Attack Vector

An attacker could potentially trigger this vulnerability by sending specially crafted RDMA over TCP packets to a system with the siw driver enabled. The malformed packets would need to cause siw_get_hdr() to fail with -EINVAL before the FPDU context is established. This could be achieved through:

• Sending packets with invalid iWARP header formats
• Crafting packets with incorrect DDP (Direct Data Placement) segment markers
• Exploiting protocol state machine edge cases during connection establishment

The KASAN splat from the kernel indicates the crash occurs at:

[  101.384271] KASAN: null-ptr-deref in range [0x00000000000000c0-0x00000000000000c7]
[  101.385869] RIP: 0010:siw_tcp_rx_data+0x13ad/0x1e50

Detection Methods for CVE-2026-23242

Indicators of Compromise

• Kernel panic or oops messages referencing siw_tcp_rx_data in the call stack
• KASAN reports showing null-ptr-deref at memory offset 0xc0-0xc7
• System crashes during RDMA over TCP/IP operations with the siw driver
• Kernel log entries showing RDMA/siw related errors followed by system instability

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for KASAN warnings related to siw module
• Enable kernel crash dump collection to capture NULL pointer dereference events
• Deploy kernel live patching monitoring to track siw driver status
• Use system monitoring tools to detect unexpected kernel module crashes or reloads

Monitoring Recommendations

• Configure kernel log monitoring for patterns matching siw_tcp_rx_data and null-ptr-deref
• Set up alerts for RDMA subsystem errors in system logs
• Monitor system stability metrics for unexpected reboots or kernel panics
• Track network interface errors on systems using siw for RDMA connectivity

How to Mitigate CVE-2026-23242

Immediate Actions Required

• Update the Linux kernel to a patched version containing the fix
• If immediate patching is not possible, consider disabling the siw kernel module if not required
• Review systems using RDMA over TCP/IP functionality to assess exposure
• Implement network segmentation to limit exposure of RDMA-enabled systems

Patch Information

The Linux kernel maintainers have released patches across multiple stable kernel branches. The fix adds a NULL pointer check to only access more_ddp_segs when rx_fpdu is present. Patches are available at:

• Kernel Stable Commit 14ab3da
• Kernel Stable Commit 714c99e
• Kernel Stable Commit 8564dcc
• Kernel Stable Commit 87b7a03
• Kernel Stable Commit ab61841
• Kernel Stable Commit ab95705
• Kernel Stable Commit ce025f7
• Kernel Stable Commit ffba40b

Workarounds

• Disable the siw kernel module if RDMA over TCP/IP functionality is not required: modprobe -r siw
• Blacklist the siw module to prevent automatic loading by adding blacklist siw to /etc/modprobe.d/blacklist.conf
• Use hardware-based RDMA adapters (InfiniBand, RoCE) instead of software iWARP if available
• Restrict network access to systems using siw driver to trusted networks only

# Disable siw module temporarily
sudo modprobe -r siw

# Permanently blacklist siw module if not needed
echo "blacklist siw" | sudo tee /etc/modprobe.d/siw-blacklist.conf

# Verify siw module is not loaded
lsmod | grep siw

# Check kernel version for patch status
uname -r