CVE-2026-74708 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
xsk: validate launch-time metadata size
Launch-time metadata extends beyond the first 16 bytes of struct xsk_tx_metadata. Reject the request when the registered metadata area does not contain the complete field.
Snapshot the validated flags for the generic transmit path and use that snapshot for request and completion processing, avoiding inconsistent decisions if user space changes the flags concurrently.
Note that only xsk_skb_metadata is properly using the flags, __xsk_buff_get_metadata ignores them. Next commits address that.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel vulnerability identified in the XDP socket (xsk) subsystem involves a critical lack of validation for launch-time metadata size during the initialization phase. Specifically, the struct xsk_tx_metadata contains fields beyond its first sixteen bytes, yet the existing implementation failed to verify that the registered user-space memory area was sufficiently large to accommodate these extended fields. This oversight allows applications to register metadata buffers that are truncated relative to what the kernel expects or requires for full functionality. When such undersized regions are utilized, subsequent operations relying on data located past the sixteenth byte may access invalid memory ranges or encounter undefined behavior, potentially leading to kernel instability or security breaches through out-of-bounds reads and writes.
From a technical perspective, this flaw represents an insufficient input validation mechanism where the boundary of allocated user-space buffers is not rigorously checked against the structural requirements of internal kernel data structures. The vulnerability aligns with CWE-131, which covers incorrect calculation of buffer size, as well as CWE-787, indicating out-of-bounds write vulnerabilities that can arise when the kernel assumes a larger buffer than actually provided by the user space application. By accepting metadata registrations without verifying their completeness, the kernel exposes itself to scenarios where partial data structures are processed, leading to potential memory corruption if subsequent code paths attempt to access fields that were not properly initialized or mapped due to the size mismatch.
The operational impact of this vulnerability extends beyond simple stability issues. An attacker with local access could exploit this flaw to trigger a denial-of-service condition by causing kernel panics through malformed metadata registrations. In more severe scenarios, if the memory layout allows for controlled overwrites, it might facilitate privilege escalation or arbitrary code execution within the kernel space. The issue is particularly insidious because it occurs during the setup phase of XDP sockets, meaning that any application utilizing this feature could inadvertently introduce a vulnerability into their environment simply by misconfiguring buffer sizes without immediate detection until runtime operations commence.
To mitigate these risks, developers have implemented strict validation logic to ensure that launch-time metadata areas contain all required fields before being accepted for use. This involves checking the size of the registered memory region against the full extent of struct xsk_tx_metadata and rejecting requests where the area is insufficient. Additionally, a snapshotting mechanism has been introduced for flags used in the generic transmit path. By capturing these flags at the time of request processing rather than reading them dynamically during completion handling, the system avoids race conditions caused by concurrent modifications from user space. This ensures consistent decision-making throughout the packet transmission lifecycle and prevents subtle logic errors that could arise from flag state changes between submission and completion phases.
Further remediation efforts are directed toward ensuring uniform usage of these validated flags across all relevant code paths. Currently, only xsk_skb_metadata correctly utilizes the snapshotted flags, while __xsk_buff_get_metadata ignores them entirely. Future patches will address this inconsistency to guarantee that security-relevant state is consistently applied throughout the XDP socket infrastructure. This holistic approach not only resolves the immediate buffer validation issue but also strengthens the overall integrity of metadata handling in high-performance networking contexts within the Linux kernel.