CVE-2025-36940 in Fuchsia
Summary
by MITRE • 08/24/2026
Use-After-Free vulnerability in a zircon kernel pager proxy (Fuchsia), which could lead to a Privilege Escalation from Userspace to Kernel (AP)
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Analysis
by VulDB Data Team • 08/24/2026
The identified security flaw represents a critical use-after-free condition within the Zircon kernel's memory management subsystem, specifically affecting the page proxy mechanism in the Fuchsia operating system. This vulnerability arises when the lifecycle of an object is not properly synchronized with its references across different execution contexts or privilege boundaries. In this specific instance, the pager proxy, which serves as a critical interface between user-space applications and the kernel's virtual memory manager, fails to correctly invalidate pointers after the underlying resource has been deallocated. This lapse in reference counting or pointer management allows an attacker who controls the state of the application to access freed memory that may have already been reallocated for other purposes. The core technical flaw lies in the asynchronous nature of page fault handling and object destruction within the kernel, where a race condition can occur between the release of a pager proxy object and subsequent operations that attempt to utilize it.
From an operational perspective, this vulnerability poses a severe risk as it facilitates privilege escalation from unprivileged user-space processes directly into the highly privileged kernel space. By exploiting the use-after-free condition, an attacker can manipulate the contents of the freed memory region or control the flow of execution through corrupted function pointers stored within the proxy object structure. This capability effectively bypasses all standard security controls and isolation mechanisms enforced by the operating system's microkernel architecture. The ability to execute arbitrary code in kernel mode grants the attacker complete control over the system, allowing for the exfiltration of sensitive data, modification of critical system configurations, or the installation of persistent rootkits that are difficult to detect and remove.
The classification of this vulnerability aligns with Common Weakness Enumeration (CWE) identifier CWE-416, which denotes Use After Free errors. These types of memory corruption bugs are particularly dangerous because they can lead to arbitrary code execution, denial of service, or information disclosure depending on how the freed memory is reused by the system. In the context of Fuchsia's capability-based security model, this flaw undermines the fundamental assumption that user-space components cannot interfere with kernel integrity through improper resource management. The vulnerability highlights a gap in the rigorous validation and lifecycle management required for objects that cross privilege boundaries within complex operating systems like Zircon.
Mitigation strategies must focus on strengthening memory safety guarantees within the Fuchsia codebase. Developers should implement strict ownership models using smart pointers or explicit lifetime annotations to ensure that no dangling references persist after an object is destroyed. Additionally, enabling kernel-level protections such as heap randomization and guard pages can reduce the exploitability of such vulnerabilities by making it harder for attackers to predict memory layouts. For immediate remediation, patching involves correcting the reference counting logic in the pager proxy implementation to prevent access once the associated resource has been released. Long-term solutions include adopting formal verification techniques or integrating static analysis tools that specifically target use-after-free patterns during the software development lifecycle to catch these issues before deployment.
This incident underscores the importance of rigorous memory safety practices even within microkernel architectures where modularity is prioritized. The ATT&CK framework categorizes such exploits under T1068, which refers to Exploitation for Privilege Escalation. Understanding this vector helps security teams prioritize monitoring and detection efforts around kernel-level anomalies that may indicate an attempt to leverage memory corruption bugs. By addressing the root cause in the Zircon pager proxy, Fuchsia can maintain its reputation as a secure, modern operating system designed with strong isolation properties between user applications and core system services.