CVE-2019-5601 in FreeBSD
Summary
by MITRE
In FreeBSD 12.0-STABLE before r347474, 12.0-RELEASE before 12.0-RELEASE-p7, 11.2-STABLE before r347475, and 11.2-RELEASE before 11.2-RELEASE-p11, a bug in the FFS implementation causes up to three bytes of kernel stack memory to be written to disk as uninitialized directory entry padding.
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Analysis
by VulDB Data Team • 10/17/2023
This vulnerability exists within the FreeBSD filesystem implementation specifically affecting the Fast File System FFS. The flaw manifests in kernel space where directory entry padding is written to disk without proper initialization, potentially exposing sensitive kernel memory contents. The vulnerability affects multiple FreeBSD release versions including 12.0-STABLE before r347474 and 12.0-RELEASE before p7, as well as 11.2-STABLE before r347475 and 11.2-RELEASE before p11. This represents a classic information disclosure vulnerability where uninitialized memory contents leak to persistent storage through the filesystem layer.
The technical root cause stems from improper handling of directory entry padding within the FFS implementation. When filesystem operations create or modify directory entries, the system allocates space for padding to maintain alignment requirements but fails to explicitly initialize this padding space before writing it to disk. This creates a scenario where residual kernel stack data from previous operations remains in memory and gets inadvertently persisted to storage devices. The vulnerability affects up to three bytes of kernel stack memory which may contain sensitive information such as cryptographic keys, session tokens, or other confidential data that was previously stored in kernel memory.
The operational impact of this vulnerability extends beyond simple information disclosure as it provides attackers with potential access to kernel memory contents that could aid in further exploitation attempts. While the exposure is limited to three bytes per directory entry, the cumulative effect across multiple directory operations could reveal substantial amounts of kernel memory. This vulnerability aligns with CWE-248, an unspecified flaw in the FFS implementation, and represents a memory safety issue that could enable attackers to gather intelligence about system memory layout and potentially aid in bypassing security mechanisms. The exposure of kernel stack contents could facilitate advanced persistent threat activities by providing attackers with insights into kernel memory organization.
From a cybersecurity perspective, this vulnerability demonstrates the critical importance of proper memory initialization in kernel space operations. The flaw represents a failure in the principle of least privilege and secure coding practices where uninitialized memory should never be written to persistent storage without explicit initialization. Organizations running affected FreeBSD systems should prioritize patching to address this vulnerability, particularly those operating in environments where kernel memory exposure could compromise system security. The remediation process involves updating to the patched versions of FreeBSD where the FFS implementation properly initializes directory entry padding before disk writes, preventing the leakage of kernel memory contents. This vulnerability also highlights the need for comprehensive memory safety testing in filesystem implementations and adherence to security standards such as those outlined in the NIST Cybersecurity Framework and ISO/IEC 27001 for information security management.