CVE-2026-80713 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
io_uring: preserve task restrictions across exec
Per-task restrictions apply to all rings created by a task. Once installed, they should not be dropped across exec.
For a task that has used io_uring, the exec cancellation path calls __io_uring_free(). This frees both the task context and the per-task restriction, so a ring created after exec is unrestricted.
Split task context cleanup into io_uring_free_tctx(), and use it from the exec cancellation path. Keep __io_uring_free() for final task cleanup, where both the context and restriction are released.
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel's io_uring subsystem manages asynchronous I/O operations by allowing user-space applications to register rings of work items that the kernel processes in a highly efficient manner. A critical aspect of this system is the enforcement of per-task restrictions, which serve as security boundaries limiting what file descriptors or resources an io_uring instance can access. These restrictions are designed to prevent privilege escalation and ensure that tasks operate within defined security contexts. However, a flaw was identified in how these restrictions were handled during process execution transitions involving the exec family of system calls. When a task utilizes io_uring and subsequently triggers an exec operation, such as replacing its current program image with a new one, the kernel's cancellation path incorrectly invoked __io_uring_free(). This function indiscriminately freed both the task context and the associated per-task restrictions. Consequently, any io_uring ring created after the exec call lacked these critical security constraints, effectively operating in an unrestricted state despite the original intent of maintaining restricted access controls throughout the lifecycle of the process's resources.
This vulnerability stems from a failure to preserve task-specific security policies across execution boundaries. In Linux, when a new program is executed via execve or similar functions, certain attributes are preserved while others are reset depending on privilege levels and configuration. The io_uring implementation failed to distinguish between temporary cleanup during an aborted exec sequence and permanent resource release upon process termination. By freeing the restrictions prematurely in the cancellation path of an exec operation, the kernel allowed subsequent I/O operations to bypass access controls that were previously enforced. This creates a scenario where a potentially untrusted or compromised binary could leverage io_uring features with broader file descriptor access than intended by the original task's security policy. The issue is particularly relevant for systems relying on strict sandboxing mechanisms like seccomp, AppArmor, or SELinux in conjunction with asynchronous I/O workloads, as it undermines the granularity of resource isolation provided by these frameworks.
The operational impact of this flaw includes potential unauthorized access to sensitive files and devices that should have been inaccessible to the executing task. An attacker exploiting this condition could read configuration files, intercept network traffic through socket operations, or interact with hardware devices beyond their permitted scope. This represents a significant security regression because it violates the principle of least privilege by granting elevated permissions without explicit authorization. The vulnerability is categorized under CWE-250, which refers to execution with unnecessary privileges, as well as CWE-732, concerning incorrect permission assignment for critical resources. From an ATT&CK perspective, this aligns with techniques involving resource hijacking and potential lateral movement if the unrestricted io_uring instance allows access to internal network services or shared storage volumes that were previously isolated.
To mitigate this vulnerability, kernel developers have restructured the cleanup logic within the io_uring subsystem. The task context cleanup process has been split into two distinct functions: io_uring_free_tctx() and __io_uring_free(). The former is now utilized in the exec cancellation path to release only the necessary task context without disturbing the per-task restrictions, thereby preserving security boundaries across exec operations. The latter function remains reserved for final task cleanup scenarios where both the context and restrictions are legitimately released upon process termination. This architectural change ensures that io_uring rings maintain their configured access controls regardless of whether they survive an execution transition or not. System administrators should ensure that kernel updates incorporating this fix are applied promptly, particularly in environments running long-lived processes with complex I/O patterns involving multiple exec calls. Regular auditing of io_uring usage and verification of permission models can further reduce exposure to similar logic flaws in asynchronous I/O implementations.