CVE-2018-20167 in Terminology
Summary
by MITRE
Terminology before 1.3.1 allows Remote Code Execution because popmedia is mishandled, as demonstrated by an unsafe "cat README.md" command when \e}pn is used. A popmedia control sequence can allow the malicious execution of executable file formats registered in the X desktop share MIME types (/usr/share/applications). The control sequence defers unknown file types to the handle_unknown_media() function, which executes xdg-open against the filename specified in the sequence. The use of xdg-open for all unknown file types allows executable file formats with a registered shared MIME type to be executed. An attacker can achieve remote code execution by introducing an executable file and a plain text file containing the control sequence through a fake software project (e.g., in Git or a tarball). When the control sequence is rendered (such as with cat), the executable file will be run.
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Analysis
by VulDB Data Team • 06/19/2023
CVE-2018-20167 represents a critical remote code execution vulnerability affecting the terminology terminal emulator version 1.3.1 and earlier. This vulnerability stems from improper handling of popmedia control sequences within the terminal application, specifically when processing escape sequences that contain file references. The flaw manifests when the \e}pn control sequence is encountered, which triggers an unsafe command execution pattern that ultimately leads to arbitrary code execution on the affected system.
The technical implementation of this vulnerability involves the misuse of the xdg-open utility through the handle_unknown_media() function within the terminology application. When a popmedia control sequence references a file, the application defers processing to xdg-open without proper validation or sanitization of the file type. This function executes xdg-open against the filename specified in the sequence, which then attempts to open the file using the user's default application based on MIME type associations. The vulnerability occurs because the system's desktop environment maintains a registry of MIME types in /usr/share/applications that can associate executable file formats with specific applications, creating a chain of execution that bypasses normal security boundaries.
This vulnerability aligns with CWE-78 and CWE-74 standards, representing a command injection flaw where user-supplied data is directly incorporated into system commands without adequate sanitization. The attack vector leverages the terminal's rendering capabilities to execute malicious payloads through carefully crafted control sequences embedded in plain text files. The exploitation process requires an attacker to create a fake software project containing both an executable file and a text file with the malicious control sequence, which when processed by commands like cat, triggers the vulnerable code path and executes the payload.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to execute arbitrary code with the privileges of the user running the terminal application. This represents a significant risk in environments where users interact with untrusted content, particularly in collaborative development environments or when processing code from external sources. The vulnerability is particularly concerning because it can be triggered through common text processing commands like cat, making it easily exploitable through routine system operations. The attack requires minimal user interaction beyond viewing the content, making it suitable for automated exploitation in phishing or supply chain attack scenarios.
Mitigation strategies should focus on implementing strict input validation for control sequences and avoiding the execution of arbitrary commands through user-supplied data. The most effective immediate fix involves updating to terminology version 1.3.1 or later, where the vulnerable popmedia handling has been properly addressed. Organizations should also consider implementing additional controls such as disabling or restricting the use of popmedia control sequences in environments where untrusted content is processed. The vulnerability demonstrates the importance of proper input sanitization and the dangers of executing system commands based on user-provided data without comprehensive validation. Network administrators should monitor for exploitation attempts and consider implementing application whitelisting policies to prevent execution of potentially malicious files through xdg-open or similar utilities.