Race Conditions

Cybersecurity 14 Sep 2026 6 min read

Filesystem Races Break the Link Between Checks and Use

A process checks that a path is safe, records a reassuring result, then opens the path a fraction of a second later. Those two operations can look like one security decision in source code. The filesystem sees two separate events, with an interval in which names, links, directories, mounts, or permissions may change. That interval is the basis of time-of-check to time-of-use races. The issue is not limited to unusually slow systems or large timing gaps. When an attacker can influence the relevant namespace concurrently, even a small gap can separate the object that passed a check from the object that receives the privileged operation.

Cybersecurity Application Security

Cybersecurity 08 Sep 2026 10 min read

Avoid Check-Then-Use Races in File Operations

A program often checks a file before using it. It may confirm that a path is inside an allowed directory, that the target is not a symbolic link, that the file belongs to an expected user, or that it does not already exist. The code then opens, replaces, deletes, or executes the file. The security problem is the gap between those two operations. If another actor can change the relevant filesystem state after the check but before the use, the program may validate one object and operate on another. This is a time-of-check to time-of-use race, often shortened to TOCTOU.

Cybersecurity Secure Coding

Cybersecurity 05 Sep 2026 10 min read

Recheck Authorization at the Point of Use

An application can perform a correct authorization check and still allow an action that should no longer be permitted. The problem appears when the application checks authority, waits or performs other work, and only later changes protected state. During that gap, the facts that justified the decision can change. For example, a worker may confirm that a user can modify a project, queue the requested change, and apply it several seconds later. If the user’s project access is revoked before the worker runs, using the earlier decision can let revoked authority survive longer than intended.

Cybersecurity Access Control

Cybersecurity 04 Sep 2026 9 min read

Make Security-Sensitive State Changes Atomic

Security checks can be individually correct and still fail when two requests run at the same time. A request checks that a recovery code is unused, a withdrawal is within a limit, or an approval is still pending. Before it records the state change, another request performs the same check against the same old state. Both requests then proceed even though the rule was meant to allow only one. This is a race condition: correctness depends on the relative timing of concurrent operations. A common form is a time-of-check to time-of-use problem, often shortened to TOCTOU, where the fact established by a check can become false before the protected action uses it.

Cybersecurity Race Conditions