CVE-2026-98323 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/siw: Bound fragmented header copies by the remaining length
siw_get_hdr() can receive an extended DDP/RDMAP header across more than one TCP callback. The first callback may receive most of the header, while the next one still limits the copy to hdrlen - MIN_DDP_HDR instead of the number of missing bytes. This makes the destination move past the end of the header and overwrite the receive state, including fpdu_part_rcvd. A later callback can then use a negative fpdu_part_rcvd value as a copy offset, which creates an OOB write.
Use the number of header bytes already received when calculating the next copy length.
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified in the Linux kernel's RDMA over Converged Ethernet (RoCE) implementation, specifically within the Software iWARP driver known as siw, represents a critical memory safety flaw rooted in improper bounds checking during network packet processing. This issue manifests when handling fragmented headers that span multiple Transmission Control Protocol callbacks. The core technical deficiency lies in the siw_get_hdr function, which is responsible for parsing extended Data Delivery Protocol or Reliable Datagram Messaging Application Protocol headers. Under normal operation, this function expects to receive header data in chunks as TCP segments arrive. However, a logical error occurs when calculating the number of bytes to copy from subsequent callbacks. Instead of determining how many missing bytes are required to complete the header structure, the code incorrectly limits the copy length based on hdrlen minus MIN_DDP_HDR. This miscalculation causes the destination pointer for the memory write operation to advance beyond the allocated boundary of the header buffer.
This out-of-bounds write directly corrupts adjacent kernel memory structures, specifically overwriting critical receive state variables such as fpdu_part_rcvd. The corruption of these internal state fields has severe operational consequences because subsequent processing logic relies on accurate values within this structure. When a later callback processes the packet stream, it utilizes the corrupted fpdu_part_rcvd value as an offset for further memory copy operations. Since this variable may now hold a negative integer due to the prior overwrite, the kernel attempts to perform a write operation using a negative index or pointer arithmetic that points outside valid memory regions. This scenario creates a classic out-of-bounds write condition, which can lead to arbitrary code execution if an attacker can control the data being written into these corrupted structures, or it may result in immediate system instability and kernel panic due to invalid memory access patterns.
From a threat modeling perspective, this vulnerability aligns with CWE-787: Out-of-bounds Write, as it involves writing data beyond the intended buffer boundary. Furthermore, because the flaw is triggered by processing network packets from potentially untrusted sources over TCP connections, it falls under the category of remote code execution vectors accessible via the network stack. In terms of MITRE ATT&CK mapping, this vulnerability facilitates techniques associated with Initial Access and Privilege Escalation, as exploitation could allow a remote attacker to bypass kernel memory protections and execute code with elevated privileges within the operating system context. The impact is particularly severe given that RDMA services are often used in high-performance computing environments where performance-critical network stacks handle large volumes of traffic, increasing the attack surface for denial-of-service or compromise attempts.
The resolution implemented by the Linux kernel maintainers addresses this flaw by correcting the logic within siw_get_hdr to properly account for the number of header bytes already received when calculating the length of data to copy in subsequent callbacks. By ensuring that the copy operation is strictly bounded by the remaining required bytes rather than an incorrect static calculation, the destination pointer remains within the allocated buffer limits. This fix prevents the overwrite of adjacent kernel structures and eliminates the possibility of negative offset calculations leading to out-of-bounds writes. To mitigate this risk in environments where immediate patching may not be feasible, administrators should restrict network access to RDMA services using strict firewall rules or VLAN segmentation to limit exposure to untrusted networks. Additionally, enabling kernel hardening features such as KASLR and stack canaries can provide additional layers of defense against exploitation attempts that might arise from similar memory corruption vulnerabilities in the future.