CVE-2025-37863 in Linux
Summary
by MITRE • 05/09/2025
In the Linux kernel, the following vulnerability has been resolved:
ovl: don't allow datadir only
In theory overlayfs could support upper layer directly referring to a data layer, but there's no current use case for this.
Originally, when data-only layers were introduced, this wasn't allowed, only introduced by the "datadir+" feature, but without actually handling this case, resulting in an Oops.
Fix by disallowing datadir without lowerdir.
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Analysis
by VulDB Data Team • 01/31/2026
The vulnerability CVE-2025-37863 affects the Linux kernel's overlay filesystem implementation and represents a security flaw in the overlayfs module that could lead to system instability. This issue specifically targets the handling of data-only layers within the overlay filesystem architecture, where the kernel fails to properly validate certain configuration scenarios that could result in system crashes or unexpected behavior. The vulnerability exists in the way overlayfs processes layer configurations, particularly when dealing with data directories that lack proper lower directory references, creating a potential denial of service condition that impacts system reliability and stability.
The technical flaw manifests in the overlay filesystem's inability to properly handle cases where a data-only layer is configured without an associated lower directory reference. This occurs during the initialization or processing of overlay filesystem mount operations where the kernel attempts to validate the layer configuration but fails to account for this specific edge case. The original implementation introduced a "datadir+" feature that was intended to support data-only layers but did not properly implement the validation logic to prevent this configuration from being processed, leading to a kernel Oops condition. This represents a classic case of incomplete input validation and improper error handling within the kernel's filesystem subsystem, where the system crashes when encountering an unexpected configuration state rather than gracefully handling the error or rejecting the invalid setup.
The operational impact of this vulnerability extends beyond simple system instability, as it could potentially be exploited by malicious actors to cause denial of service conditions or system crashes in environments that utilize overlay filesystems. The overlay filesystem is commonly used in containerization technologies, virtualization platforms, and various cloud computing environments where layered filesystems are prevalent. When exploited, this vulnerability could disrupt services running on affected systems, particularly in containerized environments where overlayfs is frequently used for image layering and storage management. The vulnerability affects systems running Linux kernels that implement overlay filesystem functionality, making it relevant to a broad range of computing environments including cloud platforms, container orchestration systems, and server deployments that rely on overlay filesystem capabilities for storage management.
Mitigation strategies for this vulnerability involve applying the kernel patches that implement the fix by disallowing datadir configurations without lowerdir references, effectively preventing the problematic scenario from being processed. System administrators should prioritize updating their Linux kernel versions to include the patched implementation that properly validates overlay filesystem configurations and rejects invalid data-only layer setups. The fix aligns with security best practices by implementing proper input validation and error handling within the kernel's filesystem subsystem, preventing the kernel from attempting to process invalid configurations that could lead to system crashes. Organizations should also consider monitoring their systems for any attempts to configure overlay filesystems with invalid layer configurations and implement proper security controls to prevent unauthorized modifications to filesystem mount options. This vulnerability demonstrates the importance of comprehensive testing and validation of filesystem configurations, particularly in complex layered storage systems where improper configurations can lead to system instability and potential security implications. The fix addresses the underlying issue by ensuring that overlayfs properly validates its configuration parameters before attempting to process them, preventing the kernel from encountering invalid states that would otherwise result in system crashes. This approach aligns with the principle of least privilege and defense in depth, ensuring that filesystem implementations reject invalid configurations rather than attempting to process them and potentially causing system failures.
This vulnerability relates to CWE-248, which covers "Uncaught Exception" in software systems, and represents a case where the kernel fails to properly handle an exceptional condition in the overlay filesystem implementation. The flaw also connects to ATT&CK technique T1499.001, which involves the exploitation of system resource exhaustion or instability through denial of service attacks, as the vulnerability can be leveraged to cause system crashes and service disruptions. The fix implemented addresses these concerns by establishing proper validation controls within the overlay filesystem subsystem, ensuring that all configuration parameters meet the required criteria before processing occurs, thereby preventing the kernel from entering an invalid state that could lead to system instability or crashes.