CVE-2025-71295 in Linux
Summary
by MITRE • 05/06/2026
In the Linux kernel, the following vulnerability has been resolved:
fs/buffer: add alert in try_to_free_buffers() for folios without buffers
try_to_free_buffers() can be called on folios with no buffers attached when filemap_release_folio() is invoked on a folio belonging to a mapping with AS_RELEASE_ALWAYS set but no release_folio operation defined.
In such cases, folio_needs_release() returns true because of the AS_RELEASE_ALWAYS flag, but the folio has no private buffer data. This causes try_to_free_buffers() to call drop_buffers() on a folio with no buffers, leading to a null pointer dereference.
Adding a check in try_to_free_buffers() to return early if the folio has no buffers attached, with WARN_ON_ONCE() to alert about the misconfiguration. This provides defensive hardening.
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Analysis
by VulDB Data Team • 07/23/2026
The vulnerability identified in the Linux kernel's buffer management subsystem represents a critical null pointer dereference condition that can lead to system instability and potential denial of service. This flaw manifests within the try_to_free_buffers() function which serves as a core component in the kernel's memory management architecture for handling file system buffers. The issue specifically occurs when the filemap_release_folio() function is invoked on folios that belong to mappings with the AS_RELEASE_ALWAYS flag enabled but lack a properly defined release_folio operation callback. This misconfiguration creates a scenario where the kernel's buffer management logic becomes inconsistent and unpredictable.
The technical root cause of this vulnerability stems from the logical inconsistency in the folio release process where folio_needs_release() returns true due to the AS_RELEASE_ALWAYS flag being set, yet the folio itself contains no actual buffer data structures. This condition creates a dangerous state where the try_to_free_buffers() function attempts to process a folio that lacks the expected buffer attachments, resulting in a direct null pointer dereference when drop_buffers() is called on an empty folio structure. The vulnerability operates at the intersection of kernel memory management and file system operations, specifically targeting the buffer cache subsystem that handles the translation between virtual memory pages and physical storage.
From an operational perspective, this vulnerability presents a significant risk to system stability and availability, particularly in environments where file system operations are frequent and diverse. The null pointer dereference can trigger kernel oops messages, system crashes, or more subtly cause memory corruption that may lead to data loss or system hangs. The impact is particularly severe in high-throughput server environments or systems with extensive file I/O operations, where the likelihood of triggering this condition increases proportionally with system load. This vulnerability falls under the category of defensive programming failures that can be exploited to cause system instability or potentially provide attackers with opportunities to escalate privileges through carefully crafted file system operations.
The mitigation strategy implemented addresses this vulnerability through defensive programming techniques that include early return conditions and warning mechanisms within the try_to_free_buffers() function. This approach aligns with established security practices for kernel development and follows the principle of least privilege by preventing dangerous operations on malformed data structures. The inclusion of WARN_ON_ONCE() provides valuable diagnostic information for system administrators and developers while maintaining system stability through graceful degradation rather than abrupt failure. This solution directly addresses the CWE-476 Null Pointer Dereference weakness and provides protection against similar classes of buffer management vulnerabilities that could arise from inconsistent kernel subsystem interactions. The fix demonstrates proper adherence to the ATT&CK framework's defensive techniques by implementing early detection and prevention mechanisms that harden the kernel against improper buffer state handling. The implementation ensures that misconfigurations in file system mappings are detected and logged appropriately without compromising system functionality, thereby maintaining the robustness of the Linux kernel's memory management subsystem while providing clear operational feedback for system maintenance and configuration correction.