CVE-2023-26421 in Acrobat Reader
Summary
by MITRE • 04/13/2023
Adobe Acrobat Reader versions 23.001.20093 (and earlier) and 20.005.30441 (and earlier) are affected by an Integer Underflow or Wraparound vulnerability that could result in arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.
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Analysis
by VulDB Data Team • 11/09/2025
Adobe Acrobat Reader contains a critical integer underflow vulnerability that stems from improper input validation within the document parsing engine. This vulnerability exists in versions 23.001.20093 and earlier, as well as 20.005.30441 and earlier, where the software fails to properly validate integer values during memory allocation operations. The flaw manifests when processing specially crafted PDF files that contain malformed integer values in their headers or metadata structures. When the application attempts to calculate memory buffer sizes based on these malformed integers, the arithmetic operation results in an underflow condition where the calculated value wraps around to a much smaller positive integer or zero. This creates a scenario where the application allocates insufficient memory for processing the document, leading to heap-based buffer overflows and potential code execution.
The vulnerability operates through a classic integer arithmetic flaw that maps to CWE-190, which specifically addresses integer overflow and underflow conditions. Attackers can exploit this weakness by crafting malicious PDF documents that contain carefully manipulated integer values in their structure. The attack requires user interaction because the target must open the malicious file within Adobe Acrobat Reader, making this a client-side exploitation vector. The underflow condition occurs during the parsing of document objects where the application computes offsets or sizes for memory allocation, particularly in areas related to font handling, image processing, or embedded object management. The specific memory corruption patterns create opportunities for attackers to manipulate the program execution flow through stack or heap corruption.
The operational impact of this vulnerability extends beyond simple privilege escalation as it allows for arbitrary code execution with the privileges of the currently logged-in user. This means that attackers who successfully exploit the vulnerability can execute malicious payloads without requiring elevated system permissions. The attack surface is significant given that Adobe Acrobat Reader is widely deployed across enterprise environments and individual workstations. The vulnerability's exploitation requires social engineering to convince users to open malicious documents, but once executed, it provides attackers with persistent access to the victim's system. The memory corruption patterns can be leveraged for various attack vectors including privilege escalation, data exfiltration, or establishing persistent backdoors within the compromised system.
Organizations should prioritize immediate patching of affected Adobe Acrobat Reader installations to mitigate this vulnerability. The recommended mitigation strategy includes deploying the latest security updates from Adobe, which address the integer underflow condition through proper input validation and bounds checking. System administrators should implement application whitelisting policies to restrict execution of untrusted PDF files and consider deploying sandboxing solutions to isolate PDF processing activities. Network-based defenses can include content filtering solutions that scan PDF files for known malicious patterns or suspicious integer structures. Security monitoring should focus on detecting unusual file access patterns or memory allocation behaviors that could indicate exploitation attempts. Additionally, user education programs should emphasize the importance of avoiding opening suspicious PDF files from untrusted sources, as the vulnerability requires user interaction to be exploited. The ATT&CK framework categorizes this as a technique involving exploitation of software vulnerabilities, specifically targeting privilege escalation and code execution through memory corruption attacks.