CVE-2017-3121 in Acrobat Reader
Summary
by MITRE
Adobe Acrobat Reader 2017.009.20058 and earlier, 2017.008.30051 and earlier, 2015.006.30306 and earlier, and 11.0.20 and earlier has an exploitable memory corruption vulnerability in the Enhanced Metafile Format (EMF) parser. Successful exploitation could lead to arbitrary code execution.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 01/08/2021
Adobe Acrobat Reader contains a critical memory corruption vulnerability within its Enhanced Metafile Format EMF parser that affects multiple versions including 2017.009.20058 and earlier, 2017.008.30051 and earlier, 2015.006.30306 and earlier, and 11.0.20 and earlier. This vulnerability stems from improper input validation and memory handling within the EMF parsing component, which processes Windows Enhanced Metafile files that can be embedded within PDF documents. The flaw manifests when the parser encounters malformed or specially crafted EMF data structures that trigger buffer overflows or heap corruption conditions during the rendering process. According to CWE-121, this represents a classic stack-based buffer overflow vulnerability that occurs when insufficient bounds checking allows attackers to write beyond allocated memory boundaries. The vulnerability falls under the ATT&CK technique T1203 - Exploitation for Client Execution, as it enables remote code execution through malicious PDF files containing crafted EMF content. When exploited successfully, the memory corruption allows attackers to execute arbitrary code with the privileges of the victim user, potentially leading to full system compromise. The attack vector typically involves social engineering campaigns where users open malicious PDF documents containing embedded EMF content, making this vulnerability particularly dangerous in enterprise environments where PDF documents are frequently shared and opened. The vulnerability is especially concerning because it affects multiple versions of Adobe Reader, indicating a widespread exposure across the user base. The technical implementation flaw lies in the lack of proper validation of EMF record lengths and structure integrity before processing, which allows attackers to craft malicious input that triggers the memory corruption. This vulnerability represents a significant risk to organizations as it can be exploited remotely through web-based attacks or via email attachments without requiring user interaction beyond opening the malicious document.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise and data exfiltration capabilities. Attackers can leverage this vulnerability to establish persistent access to target systems through the execution of malicious payloads that may include backdoors, keyloggers, or data theft utilities. The memory corruption nature of the vulnerability means that exploitation can be highly reliable and predictable, as the attacker can control the exact memory locations that get corrupted, making it easier to achieve consistent remote code execution. Security researchers have noted that this vulnerability can be combined with other exploits to create more sophisticated attack chains, potentially leading to privilege escalation or lateral movement within networks. Organizations that have not patched their Adobe Reader installations remain at significant risk, as the vulnerability can be exploited through various attack vectors including web browsers, email clients, and document viewers. The vulnerability's presence in multiple version lines indicates that it was likely introduced early in the software lifecycle and persisted through several releases due to inadequate security testing or delayed patch development. This creates a substantial window of exposure for enterprises and individuals who may not regularly update their software, making the vulnerability particularly attractive to threat actors seeking low-hanging fruit. The impact on enterprise security operations is severe, as this vulnerability can be used to bypass traditional security controls and establish a foothold for more extensive attacks.
Mitigation strategies for this vulnerability must address both immediate patching requirements and broader security posture improvements. Organizations should prioritize immediate deployment of Adobe's security patches for all affected versions of Acrobat Reader, as these updates contain fixes for the EMF parsing logic and memory handling routines. System administrators should implement network-level protections including web application firewalls and content filtering solutions that can detect and block suspicious PDF content containing embedded EMF data. The principle of least privilege should be enforced by configuring Acrobat Reader to run with minimal user permissions and by implementing sandboxing technologies that isolate PDF processing from critical system resources. Security monitoring should include detection of unusual PDF processing activity and potential exploitation attempts through behavioral analysis of user interactions with PDF documents. Organizations should also consider implementing email security solutions that can scan and quarantine potentially malicious PDF attachments before they reach end users. The vulnerability's characteristics make it particularly susceptible to automated exploitation, so organizations should deploy intrusion detection systems that can identify exploitation attempts based on known attack signatures. Regular security awareness training should emphasize the dangers of opening unexpected PDF attachments and the importance of verifying document sources before opening. Additionally, network segmentation and endpoint protection solutions should be configured to limit the potential impact if an attacker successfully exploits this vulnerability. The remediation process should include comprehensive testing of patches in controlled environments before widespread deployment to ensure compatibility with existing business applications and workflows. Long-term security improvements should involve regular vulnerability assessments and penetration testing to identify similar memory corruption issues in other software components.