Linux Kernel Vulnerability Allows Attackers to Escalate Privileges via Out-of-Bounds Write

A recently discovered vulnerability in the Linux kernel, identified as CVE-2025-0927, poses a significant threat to system security.

This flaw, present in the HFS+ file system driver, allows attackers to exploit an out-of-bounds write condition, potentially leading to local privilege escalation.

The vulnerability can be triggered by manipulating a specially crafted HFS+ filesystem, which, under certain conditions, can overwrite sensitive data in kernel space.

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CVE-2025-0927: Technical Analysis

• Vulnerability Overview: The issue arises from a buffer overflow in B-tree node processing within the hfs_bnode_read_key function in the HFS+ driver. This function fails to properly check boundary conditions for key sizes, creating an opportunity for malicious data to be written beyond allocated buffers.
• Affected Systems: The vulnerability affects Linux kernels up to version 6.12.0, including Ubuntu 22.04 with the Linux Kernel 6.5.0-18-generic.
• Exploitability: Exploiting this vulnerability requires creating a malicious HFS+ filesystem. Since mounting such a filesystem typically requires administrative privileges, the vulnerability leverages unprivileged mount capabilities allowed by certain distro configurations, particularly those that use loopback mounts.

Exploitation Strategy

To exploit CVE-2025-0927, an attacker needs to mount a specially prepared HFS+ filesystem. Below are the key steps in the exploitation process:

1. Create Malicious HFS+ Filesystem: An attacker needs to craft an HFS+ filesystem with specific attributes that trigger the vulnerability when mounted. This involves setting the attribute B-tree’s root to a null pointer and creating a file with extended attributes.
2. Mount Using “Mount Oracle”: Leverage unprivileged mount capabilities, often available in desktop environments, to mount the malicious filesystem. This “mount oracle” allows low-privileged users to mount filesystems by using tools like udisksctl.
3. Trigger Out-of-Bounds Write: Once mounted, setting an extended attribute with a lower lexicographic ordering on the malicious file triggers the out-of-bounds write condition, corrupting kernel memory.
4. Heap Spraying and KASLR Bypass: The out-of-bounds write can be used to spray objects in kernel memory, followed by exploiting the corruption to leak kernel addresses and bypass Kernel Address Space Layout Randomization (KASLR).
5. Privilege Escalation: With KASLR bypassed, attackers can manipulate sensitive data such as the modprobe path to execute arbitrary code, leading to privilege escalation.

The CVE-2025-0927 vulnerability highlights the ongoing challenges in securing modern operating systems, particularly against sophisticated attacks that target low-level system components.

The exploit relies heavily on manipulating data structures within the kernel, showcasing the complexity and skill required for such attacks.

As kernel hardening continues with improvements like RANDOMIZE_BASE and SLUB_FREELIST_RANDOM, attackers must adapt by employing more sophisticated techniques, such as cross-cache attacks.

These newer methods aim to overcome the enhanced security barriers by manipulating memory allocations across different slab caches.

Mitigation and Updates

Ubuntu has released an advisory and fixes for this vulnerability. Users are advised to update their Linux kernels to patched versions to mitigate the risk of exploitation.

Additionally, security researchers recommend a cautious approach to unprivileged mounts, advocating for stricter controls to prevent such attacks.

The CVE-2025-0927 vulnerability serves as a reminder of the intricate balance between user experience and security.

While desktop environments aim to provide ease of use by allowing unprivileged mounts, these features can also introduce vulnerabilities.

As Linux continues to evolve with enhanced security features, both developers and users must stay vigilant against emerging threats.

Update Availability

• Patch Availability: Fixes for CVE-2025-0927 are available in updated kernel versions. Users should ensure their systems are running the latest kernels to protect against this vulnerability.
• Staying Informed: Security advisories from Linux distributions and the Linux kernel community provide essential information on patches and mitigations for known vulnerabilities like CVE-2025-0927.

By addressing these vulnerabilities proactively, the Linux community demonstrates its commitment to maintaining a secure and robust operating environment.

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