CVE-1999-0724 in OpenBSD
Summary
by MITRE
Buffer overflow in OpenBSD procfs and fdescfs file systems via uio_offset in the readdir() function.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0724 represents a critical buffer overflow condition affecting the OpenBSD operating system's implementation of procfs and fdescfs file systems. This flaw manifests specifically within the readdir() function where the uio_offset parameter is improperly handled, creating a scenario where malicious input can cause memory corruption beyond the allocated buffer boundaries. The vulnerability exists in the kernel-level file system implementations that provide process and file descriptor information to userspace applications through virtual file systems.
The technical implementation of this buffer overflow stems from insufficient bounds checking in the uio_offset handling mechanism during directory read operations. When applications invoke readdir() on procfs or fdescfs mounted file systems, the system fails to validate the offset parameter against the actual buffer size allocated for directory entry data. This allows attackers to craft specially formatted directory requests that can overwrite adjacent memory locations, potentially leading to arbitrary code execution or system crashes. The vulnerability is particularly concerning because it operates at the kernel level where such memory corruption can result in complete system compromise rather than just application-level failures.
The operational impact of CVE-1999-0724 extends beyond simple denial of service scenarios, as it provides potential attackers with pathways to escalate privileges and execute malicious code with kernel-level permissions. Systems running affected OpenBSD versions become vulnerable to remote exploitation if they have procfs or fdescfs mounted and accessible to untrusted users. The vulnerability affects the core file system operations that are fundamental to process monitoring and debugging capabilities, making it particularly dangerous in environments where these file systems are actively used. Attackers could leverage this flaw to gain unauthorized access to system resources, manipulate process information, or disrupt critical system services through carefully crafted directory traversal operations.
Mitigation strategies for this vulnerability require immediate system updates and patches from OpenBSD security teams, as the flaw exists in the kernel's core file system handling code. System administrators should disable unnecessary procfs and fdescfs mounts when not required for debugging or monitoring purposes, reducing the attack surface available to potential exploiters. The implementation of proper bounds checking in the uio_offset parameter handling within the readdir() function represents the fundamental fix needed to address this issue. Security monitoring should focus on detecting unusual directory read patterns on these file systems, as such operations could indicate exploitation attempts. Organizations should also consider implementing privilege separation mechanisms to limit user access to these virtual file systems and establish regular security audits of mounted file systems to ensure compliance with security best practices. This vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and could be categorized under ATT&CK technique T1059 for command and scripting interpreter usage, particularly when exploited through process monitoring interfaces.