CVE-2003-0972 in screen
Summary
by MITRE
Integer signedness error in ansi.c for GNU screen 4.0.1 and earlier, and 3.9.15 and earlier, allows local users to execute arbitrary code via a large number of ";" (semicolon) characters in escape sequences, which leads to a buffer overflow.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability described in CVE-2003-0972 represents a critical integer signedness error that affects GNU screen versions 4.0.1 and earlier, as well as 3.9.15 and earlier. This flaw exists within the ansi.c file, which handles ANSI escape sequence processing in the terminal multiplexer. The vulnerability arises from improper handling of signed integer values when processing escape sequences containing numerous semicolon characters, creating a condition where the application fails to properly validate input length before buffer operations.
The technical implementation of this vulnerability stems from a fundamental flaw in how GNU screen processes escape sequences that contain excessive semicolon characters. When the application encounters a large number of semicolons within escape sequences, the signed integer variable used to track the sequence length becomes corrupted due to overflow conditions. This integer overflow causes the application to miscalculate buffer boundaries, ultimately leading to a classic buffer overflow condition where data written beyond the allocated buffer space. The flaw specifically manifests when the signed integer value exceeds the maximum positive value that can be represented, causing it to wrap around to a negative value that then gets interpreted as a buffer size parameter.
The operational impact of this vulnerability is severe as it enables local users to execute arbitrary code with the privileges of the affected process. This represents a privilege escalation vector that can be exploited to gain unauthorized access to system resources, potentially leading to complete system compromise. Attackers can leverage this vulnerability by crafting malicious escape sequences containing numerous semicolons, which when processed by GNU screen, trigger the buffer overflow and allow code execution. The vulnerability is particularly concerning because it affects the terminal multiplexer functionality that is commonly used in server environments and remote administration scenarios.
This vulnerability aligns with CWE-190, which describes integer overflow and underflow conditions, and more specifically with CWE-121, which addresses stack-based buffer overflow conditions. The attack pattern follows techniques described in the MITRE ATT&CK framework under T1068, which covers "Exploitation for Privilege Escalation" and T1059, covering "Command and Scripting Interpreter" for executing arbitrary code through the compromised terminal environment. The vulnerability demonstrates poor input validation practices in the processing of terminal escape sequences, where proper bounds checking should have been implemented to prevent the integer overflow condition from propagating to a buffer overflow scenario.
Mitigation strategies for this vulnerability require immediate patching of GNU screen installations to versions that address the integer signedness error in the ansi.c file. System administrators should also implement input validation measures at the terminal level to filter or limit the number of semicolons in escape sequences, particularly in environments where untrusted users have access to terminal sessions. Additional defensive measures include monitoring for unusual escape sequence patterns and implementing proper access controls to limit local user privileges where possible. The vulnerability highlights the importance of robust input validation and proper integer handling in security-critical applications, particularly those dealing with terminal processing and user input parsing.