CVE-2016-7977 in Ghostscript
Summary
by MITRE
Ghostscript before 9.21 might allow remote attackers to bypass the SAFER mode protection mechanism and consequently read arbitrary files via the use of the .libfile operator in a crafted postscript document.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2016-7977 represents a critical security flaw in Ghostscript versions prior to 9.21 that undermines the fundamental SAFER mode protection mechanism designed to prevent unauthorized file access. This vulnerability specifically targets the .libfile operator within the PostScript interpreter, which is intended to provide controlled access to system libraries while maintaining security boundaries. The flaw allows remote attackers to bypass these security controls and execute arbitrary file read operations, effectively compromising the sandboxing protections that Ghostscript implements to isolate potentially malicious code from the underlying operating system.
The technical exploitation of this vulnerability occurs through the manipulation of the .libfile operator within crafted PostScript documents that are processed by vulnerable Ghostscript implementations. When a PostScript document containing malicious .libfile directives is executed, the operator can be used to access system files that should normally be restricted under SAFER mode protection. This represents a direct violation of the security model that Ghostscript employs to prevent unauthorized file system access, as the operator essentially allows bypassing the normal file access controls that are supposed to be enforced during document processing. The vulnerability stems from insufficient validation of the .libfile operator's parameters and the lack of proper access control checks when processing these specific operators.
The operational impact of this vulnerability is significant as it enables attackers to perform unauthorized file access operations from remote locations, potentially leading to data exfiltration, system reconnaissance, and further attack escalation. Attackers can leverage this vulnerability to read sensitive files from the system, including configuration files, user data, and potentially system binaries that could provide additional attack vectors. The remote nature of the attack means that adversaries can exploit this vulnerability without requiring physical access to the target system, making it particularly dangerous in environments where Ghostscript is used to process untrusted documents from web applications or email attachments. This vulnerability directly relates to CWE-250, which addresses "Execute Code from Untrusted Input," and represents a privilege escalation issue that allows unauthorized access to system resources.
Mitigation strategies for CVE-2016-7977 primarily focus on upgrading to Ghostscript version 9.21 or later, which includes proper fixes for the SAFER mode bypass vulnerability. Organizations should also implement strict document validation and sanitization processes for any PostScript or PDF documents processed through Ghostscript, particularly when these documents originate from untrusted sources. Network-level protections such as firewalls and intrusion detection systems can help monitor for suspicious PostScript document processing activities, while application-level sandboxing should be considered as an additional defense mechanism. The vulnerability demonstrates the importance of proper operator validation in interpreter-based systems and highlights the need for comprehensive security testing of all operators and functions within sandboxed environments. This issue aligns with ATT&CK technique T1059.007 for PostScript execution and represents a critical gap in the security model that required immediate remediation to prevent unauthorized file access and data compromise across affected systems.