CVE-2026-81977 in Acrobat Reader
Summary
by MITRE • 09/09/2026
Acrobat Reader is affected by an Integer Underflow (Wrap or Wraparound) vulnerability that could lead to disclosure of sensitive memory. An attacker could leverage this vulnerability to disclose sensitive information. 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 • 09/09/2026
The identified vulnerability represents a critical security flaw within Adobe Acrobat Reader, specifically categorized as an integer underflow or wraparound error. This type of defect occurs when a calculation results in a value lower than the minimum representable value for the data type involved, causing it to wrap around to a large positive number due to how signed integers are handled in memory. In the context of Adobe Acrobat Reader, this mathematical anomaly typically arises during the processing of complex document structures or embedded objects where size calculations are performed before buffer allocation or access operations occur. When an attacker crafts a malicious file containing specifically manipulated data fields that trigger this underflow condition, the application may miscalculate the required memory bounds. This miscalculation leads to a discrepancy between the allocated buffer size and the actual amount of data being processed or accessed by the software routines.
From a technical perspective, the core issue lies in the lack of proper validation for arithmetic operations involving user-supplied input values that determine memory layout parameters. If an integer variable representing a length or offset underflows, it may result in a significantly larger positive value than intended. Consequently, subsequent memory access operations might read from or write to addresses outside the originally allocated buffer boundaries. This boundary violation allows the application to expose contents of adjacent memory regions that were not meant to be accessible by the current execution context. The vulnerability is particularly dangerous because it facilitates information disclosure, enabling an attacker to leak sensitive data such as cryptographic keys, session tokens, or other confidential information stored in the process memory space.
The operational impact of this vulnerability centers on unauthorized access to private system and application data. By exploiting the integer underflow, a threat actor can construct a proof-of-concept exploit that forces Adobe Acrobat Reader to dump portions of its heap or stack into an output stream or error message visible to the attacker. This capability effectively bypasses standard memory isolation protections, allowing for detailed reconnaissance against the target environment. The leaked information could serve as a stepping stone for further attacks, such as defeating address space layout randomization (ASLR) by revealing base addresses of loaded libraries, thereby increasing the success rate of subsequent code execution attempts. Although the primary impact is disclosure rather than direct remote code execution, the intelligence gained can be instrumental in developing more sophisticated exploits that lead to full system compromise.
Exploitation of this vulnerability requires a degree of user interaction, as it necessitates that the victim opens or renders a maliciously crafted PDF file within Adobe Acrobat Reader. This requirement places the burden on end-user awareness and organizational security policies regarding document handling. Attackers typically distribute these files through phishing campaigns, drive-by downloads, or compromised websites where users are tricked into opening attachments or clicking links that trigger automatic rendering of the payload. Once opened, the malicious content is processed by the reader engine, triggering the integer underflow condition during parsing routines. The severity of this requirement means that while automated worm-like propagation is unlikely, targeted attacks against specific individuals or organizations remain a significant threat vector.
To mitigate the risks associated with this vulnerability, it is imperative to apply all available security patches and updates provided by Adobe promptly. These updates typically include code changes that enforce strict validation checks on integer arithmetic operations before they are used for memory management decisions. Organizations should also implement application control policies to restrict the execution of untrusted scripts or macros within PDF files if such features are enabled. Additionally, deploying network-level protections such as web proxies with sandboxing capabilities can help detect and block attempts to deliver malicious documents containing known exploit patterns. User education remains a critical component of defense in depth, emphasizing caution when opening attachments from unknown sources.
From an industry standard classification perspective, this vulnerability aligns with CWE-192, which defines integer coercion errors that lead to wraparound conditions. It also relates closely to CWE-787, out-of-bounds write or read vulnerabilities, as the underflow directly causes memory access violations beyond allocated boundaries. In terms of tactical mapping within the MITRE ATT&CK framework, this exploit technique falls under T1059, Command and Scripting Interpreter, specifically when used in conjunction with other techniques to facilitate information gathering via T1005, Data from Local System. Understanding these classifications helps security teams prioritize remediation efforts based on established threat models and common attack patterns observed across the industry. Continuous monitoring for anomalous behavior in document processing applications can further aid in detecting potential exploitation attempts before significant damage occurs.