CVE-2026-88361 in SumatraPDF
Summary
by MITRE • 09/24/2026
SumatraPDF 3.6.1 contains an integer overflow vulnerability in EngineMupdf::BuildPageLabelRec() when parsing PDF PageLabels /Nums entries.
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Analysis
by VulDB Data Team • 09/25/2026
The security flaw identified in SumatraPDF version 3.6.1 resides within the core rendering engine, specifically affecting the function responsible for constructing page label records during the processing of Portable Document Format files. This vulnerability is categorized as an integer overflow, a type of error that occurs when an arithmetic operation produces a result too large to be represented by the allocated data type. In this specific context, the issue arises while parsing the /Nums entries within the PageLabels dictionary object of a PDF document. The application fails to adequately validate or constrain numerical values before performing calculations related to page numbering and labeling structures. When an attacker crafts a malicious PDF containing specially constructed numeric inputs for these entries, the internal arithmetic operations can exceed the maximum limit of the integer variable used by the software. This miscalculation leads to incorrect memory allocation sizes or buffer boundaries being calculated based on wrapped-around negative values or excessively large positive numbers that do not reflect the actual intended size.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration identifier CWE-190, which defines integer overflow or wraparound errors. The lack of proper bounds checking allows an attacker to manipulate how much memory is allocated for subsequent operations involving page label data structures. If the resulting calculation leads to a smaller allocation than required by the actual input size, it creates conditions ripe for a buffer overflow when data is written into that undersized buffer. Alternatively, if the logic proceeds with incorrect assumptions about array indices or loop counters derived from these corrupted values, it may result in out-of-bounds memory access. Such scenarios can lead to arbitrary code execution, denial of service through application crashes, or information disclosure depending on how the operating system and runtime environment handle the resulting invalid memory operations. The vulnerability highlights a critical gap in input validation within the PDF parsing module, where numeric fields are not rigorously checked against expected ranges before being used in computational logic that dictates resource allocation.
The operational impact of this flaw is significant for users who rely on SumatraPDF to view documents from untrusted sources or automated systems processing large volumes of PDFs. An attacker could distribute a maliciously crafted PDF via email, web download, or file sharing platforms. Upon opening the document within the vulnerable version of SumatraPDF, the application would attempt to process the malformed PageLabels entry. The resulting integer overflow could cause the software to crash immediately, leading to a denial of service for the user. More critically, if the memory corruption allows control over execution flow, it enables remote code execution with the privileges of the current user. This poses severe risks in enterprise environments where employees may inadvertently open phishing attachments or compromised documents hosted on malicious websites. The exploitability is heightened by the fact that PDF parsing often occurs automatically upon file opening without requiring additional macro activation steps common in Microsoft Office exploits.
To mitigate this risk, users should immediately upgrade to a patched version of SumatraPDF released after the identification and resolution of CVE details related to integer overflows in page label processing. Administrators managing endpoints with SumatraPDF installed should enforce software update policies to ensure all instances are running secure versions. Additionally, organizations can implement network-level controls such as sandboxing PDF viewers or using content disarming and reconstruction tools that strip potentially dangerous objects from documents before they reach the end-user application. Security teams should also monitor for indicators of compromise associated with exploit attempts targeting this specific vulnerability class in document parsers. Future development efforts must prioritize rigorous input validation, specifically ensuring that all numeric values extracted from external file formats are validated against strict bounds and type constraints prior to any arithmetic operations or memory allocation decisions. Adhering to secure coding practices aligned with CWE-190 guidelines will prevent similar integer manipulation flaws in other components of the software stack.