CVE-2026-74707 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
xsk: validate metadata when processing requests
The zero-copy path validates TX metadata while obtaining the descriptor context, then reads it again later when preparing the hardware request. User space can change the metadata between those operations and bypass the original validation.
Validate the metadata in xsk_tx_metadata_request() and use the resulting flags snapshot for every feature check. Read request fields once so all zero-copy drivers process only values observed after successful validation.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel's XDP socket (xsk) subsystem, which facilitates high-performance network packet processing by allowing user-space applications to bypass the traditional kernel networking stack, contained a logic flaw in its transmission path that allowed for metadata tampering. This vulnerability specifically affects the zero-copy mechanism where data descriptors are passed directly between user space and the kernel without intermediate copying. The core issue stems from a race condition inherent in how transactional state is handled during request processing. When an application submits a transmission request, the kernel initially validates the associated TX metadata to ensure it meets security and operational constraints. However, rather than locking this validated state for the duration of the hardware preparation process, the system re-reads the metadata from user space later when constructing the actual hardware descriptor. This temporal gap between validation and usage creates an opportunity for a malicious or compromised user-space application to modify the metadata fields after they have been checked but before they are applied by the network driver.
This design flaw effectively allows user-space processes to bypass security validations that were intended to restrict certain operations based on metadata flags. By altering these values in memory between the validation step and the hardware submission step, an attacker can trick the kernel into processing requests with invalid or dangerous configurations. For instance, this could involve manipulating flags that control buffer ownership, packet length limits, or offload capabilities. The consequence is a potential violation of system integrity where user-space code executes actions that were explicitly denied during the initial security check. This undermines the trust boundary between privileged kernel space and unprivileged user space, potentially leading to denial-of-service conditions through malformed hardware requests or, in more complex scenarios involving specific driver implementations, arbitrary memory access if the metadata controls buffer pointers or sizes without subsequent re-verification against safe bounds.
From a technical classification perspective, this vulnerability aligns with CWE-367, Time-of-check Time-of-use (TOCTOU) Race Condition. The flaw arises because the check for valid metadata is not atomic with respect to its use in hardware preparation. Furthermore, it relates to CWE-20, Improper Input Validation, as the system fails to ensure that the data used matches the validated input due to external modification during processing. In terms of adversary tactics, this could be leveraged within an ATT&CK framework context under techniques such as T1059 Command and Scripting Interpreter if it allows for further exploitation leading to code execution, or more broadly under privilege escalation vectors where a lower-privileged user-space process gains the ability to perform actions reserved for higher privileges by subverting kernel-side validation logic. The impact is primarily localized to systems utilizing XDP sockets with zero-copy transmission features enabled, particularly those running high-throughput network applications that rely on this path for performance optimization.
The resolution implemented in the Linux kernel addresses this issue by enforcing strict consistency between validation and usage. The fix introduces a mechanism where metadata flags are captured into a local snapshot immediately after successful validation within the xsk_tx_metadata_request function. This snapshot is then used exclusively for all subsequent feature checks and hardware request preparations, ensuring that no external modifications can alter the operational parameters mid-process. Additionally, the patch mandates reading request fields only once per operation cycle to guarantee that zero-copy drivers process values that were observed after successful validation. This approach eliminates the race window by decoupling the dynamic user-space memory from the static kernel-side decision logic during critical sections of packet transmission.
To mitigate similar risks in other systems or while applying this patch, administrators and developers should ensure that all network stack components are updated to versions containing these fixes. For organizations relying on high-performance networking stacks like DPDK or XDP-based applications, it is crucial to verify that the underlying kernel version includes the corrected xsk_tx_metadata_request logic. Security teams should monitor for any anomalous behavior in network interfaces associated with sudden spikes in errors or dropped packets, which might indicate exploitation attempts targeting this race condition. Furthermore, principle of least privilege should be strictly enforced on user-space applications interacting with XDP sockets to minimize the blast radius if a vulnerability is discovered in other parts of the stack. Regular auditing of kernel patches and timely application of security updates remain the primary defense against such logic flaws that exploit timing discrepancies in system calls.