CVE-1999-0035 in IRIX
Summary
by MITRE
Race condition in signal handling routine in ftpd, allowing read/write arbitrary files.
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Analysis
by VulDB Data Team • 04/16/2026
The vulnerability described in CVE-1999-0035 represents a critical race condition within the signal handling mechanism of the ftpd daemon, a fundamental component of internet file transfer services. This flaw exists in the traditional Unix-based ftpd implementation where the service processes signals during file operations, creating a temporal window where concurrent execution paths can lead to unpredictable behavior. The race condition specifically manifests when the ftpd process receives signals while executing file operations, particularly those involving file creation, modification, or access. The underlying issue stems from improper synchronization between signal delivery and file operation execution contexts, allowing attackers to manipulate the timing of signal processing to interfere with file system operations.
The technical implementation of this vulnerability exploits the fundamental weakness in how the ftpd daemon manages signal delivery during critical file operations. When a signal is received while the daemon is in the process of opening, reading, or writing files, the signal handler can interrupt the ongoing operation at an inopportune moment. This interruption can cause the daemon to open files with incorrect permissions, access unintended file descriptors, or perform operations on files that have been modified by other processes or users. The race condition typically occurs when the daemon is processing a file transfer operation and simultaneously receives a signal that triggers a signal handler routine. The flaw allows attackers to manipulate the timing of these events to force the daemon into opening arbitrary files or performing operations on files that they should not have access to, essentially bypassing normal file access controls through temporal manipulation.
The operational impact of this vulnerability extends far beyond simple unauthorized file access, creating potential for complete system compromise and data exfiltration. An attacker exploiting this race condition can potentially read sensitive system files, write malicious content to critical system locations, or manipulate file permissions to gain elevated privileges. The vulnerability is particularly dangerous because it operates at the daemon level, meaning successful exploitation can provide persistent access to the system through the ftpd service. Attackers can leverage this flaw to establish backdoors, modify system binaries, or access confidential data stored in files that should normally be protected. The race condition makes detection particularly challenging since the vulnerability manifestation depends on precise timing and system state conditions that may not be easily reproducible in controlled environments.
Mitigation strategies for CVE-1999-0035 require immediate implementation of both operational and architectural solutions to address the fundamental race condition in signal handling. The most effective immediate fix involves implementing proper signal masking and blocking during critical file operations, ensuring that signal handlers do not interrupt file system calls at inappropriate moments. System administrators should disable unnecessary ftpd services or implement proper access controls and network segmentation to limit exposure. The vulnerability aligns with CWE-362, which specifically addresses race conditions in concurrent programming, and relates to ATT&CK technique T1078 for valid accounts and T1566 for malicious file execution. Organizations should consider upgrading to modern secure file transfer implementations that properly handle signal delivery and file operations, as the traditional ftpd daemon has numerous security limitations. Regular security auditing and monitoring of signal handling routines in critical system services can help identify similar race conditions that may exist in other components of the system infrastructure.