CVE-2018-20969 in Patch
Summary
by MITRE
do_ed_script in pch.c in GNU patch through 2.7.6 does not block strings beginning with a ! character. NOTE: this is the same commit as for CVE-2019-13638, but the ! syntax is specific to ed, and is unrelated to a shell metacharacter.
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Analysis
by VulDB Data Team • 11/26/2023
The vulnerability identified as CVE-2018-20969 represents a significant security flaw in the GNU patch utility version 2.7.6 and earlier, specifically within the do_ed_script function located in the pch.c source file. This issue arises from inadequate input validation mechanisms that fail to properly sanitize or reject potentially dangerous string inputs that begin with the exclamation mark character. The vulnerability is particularly concerning because it leverages the ed script command syntax, which allows for command execution within the patch processing context, creating a potential attack vector for privilege escalation or arbitrary code execution.
The technical flaw stems from the improper handling of strings that commence with the ! character, which is a legitimate syntax element in ed script processing. When GNU patch encounters such strings during script execution, it fails to adequately filter or escape these inputs before processing them, potentially allowing malicious actors to inject ed commands that could execute arbitrary system commands. This behavior directly violates fundamental security principles of input sanitization and command injection prevention, as outlined in CWE-78 and CWE-88 categories. The vulnerability operates at the command injection level, where untrusted input is interpreted and executed as shell commands, making it particularly dangerous in environments where patch utilities are used with untrusted input data.
The operational impact of this vulnerability extends beyond simple command execution, as it can be exploited to compromise systems running affected versions of GNU patch. Attackers could craft malicious patch files containing strings beginning with ! that, when processed by the vulnerable patch utility, would execute unintended commands with the privileges of the user running the patch command. This could lead to privilege escalation, data exfiltration, or complete system compromise, depending on the execution context and system permissions. The vulnerability is particularly problematic in automated build environments, package management systems, or any scenario where patch files are applied without proper input validation, as it can be exploited through seemingly benign patch operations.
Security mitigations for CVE-2018-20969 primarily involve upgrading to GNU patch version 2.7.7 or later, where the input validation has been properly implemented to reject strings beginning with the ! character. Organizations should also implement strict input validation measures when processing patch files, including sanitizing or rejecting any input containing potentially dangerous syntax elements. The mitigation strategy aligns with ATT&CK technique T1059.001 for command and scripting interpreter execution, emphasizing the importance of preventing untrusted input from being interpreted as executable commands. Additionally, system administrators should consider implementing least privilege principles when running patch utilities and monitor for suspicious patch application activities that could indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation in security-critical utilities and highlights the need for comprehensive testing of edge cases in command-line tool implementations.