CVE-2025-40333 in Linux
Summary
by MITRE • 12/09/2025
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix infinite loop in __insert_extent_tree()
When we get wrong extent info data, and look up extent_node in rb tree, it will cause infinite loop (CONFIG_F2FS_CHECK_FS=n). Avoiding this by return NULL and print some kernel messages in that case.
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Analysis
by VulDB Data Team • 07/09/2026
The vulnerability CVE-2025-40333 represents a critical flaw in the Linux kernel's F2FS (Flash-Friendly File System) implementation that can lead to system instability and potential denial of service conditions. This issue specifically affects the __insert_extent_tree() function within the F2FS subsystem, which is responsible for managing extent information data structures that track file allocation patterns on flash storage devices. The vulnerability arises from improper handling of corrupted or malformed extent metadata during tree traversal operations, creating a scenario where the kernel's extent management logic can become trapped in an infinite loop.
The technical root cause of this vulnerability lies in the rb tree (red-black tree) traversal mechanism used by F2FS to organize and manage extent information. When the system encounters corrupted extent data during a lookup operation, the rb tree traversal logic fails to properly validate the integrity of the extent_node structures it encounters. This failure results in a condition where the tree traversal algorithm continuously cycles through the same set of nodes without reaching a termination point, effectively creating an infinite loop that consumes CPU resources and prevents normal system operation. The vulnerability is particularly concerning because it only manifests when the CONFIG_F2FS_CHECK_FS kernel configuration option is disabled, meaning systems with default security settings may be vulnerable to exploitation without explicit detection mechanisms.
The operational impact of this vulnerability extends beyond simple system performance degradation to potentially complete system lockup or crash scenarios. When the infinite loop occurs during file system operations, it can cause the kernel to become unresponsive, preventing further file system access and potentially leading to system-wide hangs that require manual intervention or system reboot. This behavior directly violates the fundamental reliability requirements for operating system components and can be exploited by malicious actors to perform denial of service attacks against systems running F2FS file systems. The vulnerability affects systems using F2FS as their primary file system, particularly those deployed in embedded systems, mobile devices, and storage appliances where flash-based storage is prevalent.
From a cybersecurity perspective, this vulnerability aligns with CWE-835, which addresses infinite loops or iterations in software implementations, and represents a classic example of how improper error handling can lead to system instability. The ATT&CK framework categorizes this as a system resource exhaustion technique where an attacker can consume CPU cycles indefinitely, potentially leading to service disruption. The vulnerability demonstrates the importance of robust input validation and error handling in kernel space operations, as the lack of proper bounds checking and data integrity verification in the extent tree management code creates a pathway for malicious exploitation. Organizations should prioritize immediate patching of this vulnerability through kernel updates, while also implementing monitoring for unusual CPU usage patterns that might indicate the occurrence of this infinite loop condition.
The mitigation strategy involves enabling the CONFIG_F2FS_CHECK_FS configuration option to provide additional validation checks that would prevent the infinite loop condition from occurring, though this may introduce performance overhead. System administrators should also implement comprehensive monitoring solutions that can detect anomalous CPU utilization patterns, particularly during file system operations, to identify potential exploitation attempts. Additionally, maintaining up-to-date kernel versions and conducting regular security assessments of systems using F2FS file systems will help prevent exploitation of this vulnerability. The fix implemented in the kernel ensures that when malformed extent data is detected, the system returns NULL instead of entering the infinite loop while generating appropriate kernel log messages to aid in forensic analysis and debugging efforts.