CVE-2021-45944 in GhostPDL
Summary
by MITRE • 01/01/2022
Ghostscript GhostPDL 9.50 through 9.53.3 has a use-after-free in sampled_data_sample (called from sampled_data_continue and interp).
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-45944 represents a critical use-after-free flaw within the Ghostscript GhostPDL library version 9.50 through 9.53.3. This issue manifests in the sampled_data_sample function which is invoked by both sampled_data_continue and interp functions within the rendering pipeline. The vulnerability arises from improper memory management where freed memory locations are accessed after being deallocated, creating potential attack vectors for remote code execution and system compromise. The affected software components operate within the broader context of PostScript and PDF rendering systems, making this flaw particularly dangerous as it can be triggered through maliciously crafted documents processed by Ghostscript.
The technical implementation of this use-after-free vulnerability stems from the improper handling of memory allocation and deallocation within the sampled data processing functions. When the sampled_data_sample function executes, it processes image data samples that are typically part of PDF or PostScript document rendering. The flaw occurs during the transition between memory allocation and deallocation phases where the interpreter continues to reference memory that has already been freed. This condition allows attackers to potentially control the memory layout and execute arbitrary code through carefully crafted input that triggers the vulnerable code path. The CWE-416 identifier applies directly to this vulnerability, representing the specific category of use-after-free conditions that occur when memory is accessed after it has been freed by a program.
The operational impact of this vulnerability extends beyond simple memory corruption as it enables sophisticated attack scenarios including remote code execution, privilege escalation, and denial of service conditions. Attackers can exploit this flaw by crafting malicious PDF or PostScript documents that, when processed by vulnerable Ghostscript versions, trigger the memory corruption. The attack surface is particularly broad given that Ghostscript is widely deployed in enterprise environments, web applications, and document processing systems. The vulnerability's exploitation can lead to complete system compromise, data exfiltration, and persistent backdoor installation, making it a high-priority target for threat actors. This aligns with ATT&CK technique T1059.007 for command and script interpreter usage and T1068 for exploit for privilege escalation.
Mitigation strategies for CVE-2021-45944 require immediate patching of affected Ghostscript installations to versions 9.54.0 or later where the memory management issues have been resolved. Organizations should implement strict input validation and sandboxing measures when processing untrusted documents, particularly in web-facing applications. Network segmentation and access controls should be enforced to limit exposure of systems running Ghostscript. Security monitoring should include detection of suspicious document processing activities and memory access patterns. Regular vulnerability assessments and penetration testing should be conducted to identify similar memory corruption issues in other components of the document processing stack. Additionally, implementing automated patch management systems ensures timely deployment of security updates across all affected systems while maintaining proper system integrity and availability.