CVE-2018-16802 in Ghostscript
Summary
by MITRE
An issue was discovered in Artifex Ghostscript before 9.25. Incorrect "restoration of privilege" checking when running out of stack during exception handling could be used by attackers able to supply crafted PostScript to execute code using the "pipe" instruction. This is due to an incomplete fix for CVE-2018-16509.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2018-16802 represents a critical privilege escalation flaw within Artifex Ghostscript versions prior to 9.25. This issue stems from inadequate privilege checking mechanisms during exception handling scenarios, specifically when the system encounters stack exhaustion conditions. The flaw manifests when Ghostscript processes malicious PostScript code that triggers exception handling routines, creating a pathway for attackers to execute arbitrary code with elevated privileges. The vulnerability is particularly concerning because it leverages the pipe instruction, a feature designed for system command execution, making it a direct vector for command injection attacks. This weakness directly impacts the software's ability to maintain proper security boundaries during error conditions, potentially allowing unprivileged users to gain elevated system access.
The technical implementation of this vulnerability occurs within Ghostscript's exception handling subsystem where privilege restoration checks are insufficiently enforced. When the system runs out of stack space during exception processing, the privilege checking mechanism fails to properly validate the security context, allowing malicious code execution through the pipe instruction. This represents a regression in security controls, as the issue stems from an incomplete fix for a similar vulnerability CVE-2018-16509, demonstrating poor remediation practices in the software development lifecycle. The flaw operates at the intersection of memory management and privilege control, where stack exhaustion triggers improper privilege validation, creating an exploitable condition that bypasses normal security controls. The pipe instruction, which normally requires explicit privilege escalation, becomes accessible through this exception handling flaw, enabling attackers to execute system commands directly.
The operational impact of CVE-2018-16802 extends beyond simple code execution to encompass full system compromise in environments where Ghostscript processes untrusted PostScript content. This vulnerability affects applications that utilize Ghostscript for document rendering, conversion, or processing, including web applications, document management systems, and print servers. Attackers can exploit this vulnerability by crafting malicious PostScript files that trigger stack exhaustion during processing, leading to privilege escalation and potential system takeover. The vulnerability's exploitation requires only the ability to submit crafted PostScript content, making it particularly dangerous in environments where users can upload or submit documents for processing. This threat model aligns with attack patterns documented in the attack tree framework, where privilege escalation vulnerabilities serve as stepping stones for more extensive system compromise. The vulnerability also presents challenges for defense-in-depth strategies as it occurs within the core processing logic rather than at network boundaries or user interfaces.
Mitigation strategies for CVE-2018-16802 primarily focus on immediate software updates to Ghostscript 9.25 or later versions where the vulnerability has been properly addressed. Organizations should implement strict content validation and sanitization procedures for all PostScript files processed by Ghostscript, including mandatory file format verification and size limitations. Network segmentation and privilege separation can help limit the potential impact of successful exploitation by reducing the privileges available to Ghostscript processes. Additionally, monitoring systems should be configured to detect unusual process behavior or command execution patterns that might indicate exploitation attempts. The fix addresses the root cause by implementing proper privilege restoration checks during exception handling scenarios, preventing the bypass of security controls that occurred in earlier versions. This remediation aligns with security best practices outlined in the CWE catalog under weakness category 254, which addresses security features that are not properly implemented. Organizations should also consider implementing sandboxing techniques and application whitelisting to further reduce the attack surface and limit potential damage from exploitation attempts.