CVE-2026-74694 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
net/ncsi: fix heap OOB read in NCSI_CMD_SEND_CMD payload length
ncsi_send_cmd_nl() takes the number of bytes to copy from the attacker-controlled ncsi_pkt_hdr.length field of the in-band packet header, while the source buffer is the NCSI_ATTR_DATA netlink attribute whose readable size is nla_len() - sizeof(ncsi_pkt_hdr). The two length sources are never cross-checked: only nla_len() >= sizeof(struct ncsi_pkt_hdr) is enforced.
With hdr->length set larger than the attribute payload (up to 65535 against at most 2032 readable bytes), ncsi_cmd_handler_oem() copies past the end of the netlink attribute buffer with unsafe_memcpy(), leaking up to ~64KB of kernel heap memory into the transmitted NCSI command packet. The destination skb is sized by the declared payload, so the write side does not overflow - this is a pure OOB read / information leak, reachable with CAP_NET_ADMIN on systems with a registered NCSI device (e.g. OpenBMC on Aspeed BMC SoCs, where NET_NCSI=y is standard).
Reject commands whose declared payload extends past the end of the data attribute.
The issue was found by the autokbug dynamic kernel fuzzer at Tencent Yunding Lab.
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Analysis
by VulDB Data Team • 08/22/2026
A critical heap out-of-bounds read vulnerability has been identified within the Linux kernel's Network Controller Sideband Interface subsystem, specifically affecting the net/ncsi module. This flaw resides in the ncsi_send_cmd_nl function, which is responsible for processing network control commands sent via Netlink attributes. The core technical deficiency involves a failure to validate the payload length declared by an attacker against the actual size of the data buffer provided through the NCSI_ATTR_DATA attribute. Specifically, the function extracts the number of bytes to copy from the ncsi_pkt_hdr.length field contained within the packet header supplied by the user space process. However, this value is not cross-checked against the readable size of the source buffer, which is determined by subtracting the size of the header structure from the total length returned by the nla_len macro. The existing validation logic only ensures that the attribute payload is large enough to contain the header itself, leaving a significant gap in boundary checking for the actual data content.
The operational impact of this vulnerability allows an attacker with CAP_NET_ADMIN privileges on a system equipped with NCSI hardware support, such as OpenBMC deployments on Aspeed BMC SoCs where NET_NCSI is enabled, to read arbitrary kernel heap memory. By setting the hdr->length field in the packet header to a value significantly larger than the actual attribute payload—potentially up to 65535 bytes against a maximum readable limit of approximately 2032 bytes—the attacker triggers an unsafe memcpy operation that reads past the end of the allocated buffer. This results in the leakage of kernel heap data into the transmitted NCSI command packet, effectively creating an information disclosure channel. Although the destination socket buffer is sized according to the declared payload preventing a write-side overflow, the read side remains vulnerable, leading to the exposure of sensitive memory contents that may include cryptographic keys, session tokens, or other privileged system state.
From a classification perspective, this vulnerability aligns with CWE-125, which describes Out-of-bounds Read conditions where software reads data past the end, or before the beginning, of the intended buffer. In terms of attack vectors and techniques, it corresponds to ATT&CK technique T1083, File and Directory Discovery, as well as general information leakage patterns often associated with improper input validation in network-facing services. The vulnerability is particularly severe due to its reachability via standard administrative capabilities rather than requiring root access or physical interaction, making it a viable target for privilege escalation chains or lateral movement within compromised environments that utilize NCSI interfaces for hardware management.
The resolution involves implementing strict length verification logic before performing the memory copy operation. Developers must ensure that the payload length specified in the packet header does not exceed the remaining size of the netlink attribute after accounting for the header structure itself. This fix prevents the unsafe memcpy from accessing memory outside the bounds of the allocated buffer, thereby eliminating the information leak vector. Systems running affected kernel versions should be updated to incorporate this patch immediately. Additionally, administrators should review access controls around NCSI interfaces and ensure that only trusted processes with appropriate capabilities can interact with these network control endpoints, mitigating the risk even in environments where immediate patching might be delayed due to operational constraints.