CVE-2005-4890 in shadow
Summary
by MITRE
There is a possible tty hijacking in shadow 4.x before 4.1.5 and sudo 1.x before 1.7.4 via "su - user -c program". The user session can be escaped to the parent session by using the TIOCSTI ioctl to push characters into the input buffer to be read by the next process.
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Analysis
by VulDB Data Team • 02/04/2024
The vulnerability described in CVE-2005-4890 represents a critical security flaw in Unix-like operating systems that allows for unauthorized session hijacking through improper handling of terminal input streams. This issue affects shadow password suite versions 4.x prior to 4.1.5 and sudo versions 1.x prior to 1.7.4, specifically when executing commands through the su command with the -c option. The vulnerability stems from a fundamental flaw in how these utilities manage terminal input buffers during command execution, creating an exploitable condition that can be leveraged by malicious actors to gain elevated privileges or access unauthorized sessions.
The technical exploitation of this vulnerability relies on the TIOCSTI ioctl system call, which allows processes to inject characters into the terminal input buffer of another process. When a user executes a command using "su - user -c program", the system creates a new session context where the target user's environment is established. However, due to insufficient input buffer management, an attacker can utilize the TIOCSTI ioctl to push pre-defined character sequences into the input stream that would normally be processed by the parent session. This allows the attacker to effectively escape the controlled execution environment and gain access to the parent session's terminal input, potentially enabling them to execute commands in the context of the original user or even escalate privileges beyond what should be permitted.
The operational impact of this vulnerability extends far beyond simple session hijacking, as it can be leveraged to bypass security controls designed to isolate user sessions and prevent unauthorized access to sensitive system resources. According to CWE-284, this vulnerability represents an improper access control issue where the system fails to properly validate and manage terminal input streams during privilege escalation operations. The attack vector specifically targets the terminal session management mechanism, which is a critical component of Unix security architecture. This vulnerability can be particularly dangerous in multi-user environments where administrative access is required, as it allows for unauthorized privilege escalation without proper authentication mechanisms being triggered.
From an ATT&CK framework perspective, this vulnerability maps to several techniques including privilege escalation through TIOCSTI ioctl manipulation, which falls under T1068 (Local Privilege Escalation) and T1548.003 (Evasion: Sudo and Sudo Caching). The exploitation pattern aligns with T1059 (Command and Scripting Interpreter) as attackers can inject commands into the terminal buffer to execute arbitrary code. Additionally, this vulnerability demonstrates weaknesses in T1078 (Valid Accounts) where legitimate user accounts can be compromised through manipulation of session control mechanisms rather than through direct credential theft.
The recommended mitigations for this vulnerability involve updating affected systems to versions that properly implement input buffer management during session switching operations. System administrators should ensure that shadow utilities are updated to version 4.1.5 or later and sudo is upgraded to version 1.7.4 or higher. Additionally, implementing proper session isolation controls and monitoring for unauthorized TIOCSTI ioctl usage can help detect potential exploitation attempts. The vulnerability highlights the importance of proper input validation and stream management in privileged operations, emphasizing that terminal session management requires careful attention to prevent such low-level input buffer manipulation attacks that can bypass traditional security controls and authentication mechanisms.