CVE-2026-88361

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Integer Overflow in SumatraPDF PDF PageLabels Parsing

Publication date: 2026-09-24

Last updated on: 2026-09-25

Assigner: MITRE

Description

SumatraPDF 3.6.1 contains an integer overflow vulnerability in EngineMupdf::BuildPageLabelRec() when parsing PDF PageLabels /Nums entries.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-09-24

Last Modified

2026-09-25

Generated

2026-10-14

AI Q&A

2026-09-24

EPSS Evaluated

2026-10-13

NVD

CVE-2026-88361

EUVD

EUVD-2026-86287

Affected Vendors & Products

Vendor	Product	Version / Range
mupdf	mupdf	1.28.0-rc2
sumatrapdf	sumatrapdf	3.6.1

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-190	The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Attack-Flow Graph

Executive Summary

SumatraPDF 3.6.1 has an integer overflow vulnerability in the function EngineMupdf::BuildPageLabelRec() when processing PDF PageLabels /Nums entries. An attacker can exploit this by setting a /Nums key to INT_MAX (2147483647), causing an overflow when adding 1 to the value. This leads to undefined behavior and potential crashes, especially in builds with undefined behavior sanitizers.

Detection Guidance

To detect this vulnerability, monitor for crashes in SumatraPDF when processing PDFs with PageLabels /Nums keys set to INT_MAX. Check application logs for SIGILL signals in builds with undefined behavior sanitizers. Inspect PDFs for malicious PageLabels entries using tools like pdfinfo or custom scripts parsing PDF structure.

Impact Analysis

This vulnerability could allow an attacker to crash SumatraPDF or other mupdf-based viewers by providing a malicious PDF with a specially crafted PageLabels /Nums key. The crash occurs due to integer overflow leading to undefined behavior, which may trigger SIGILL signals in certain builds.

Compliance Impact

This vulnerability does not directly affect compliance with GDPR, HIPAA, or similar standards as it is a technical flaw in PDF rendering software that could lead to application crashes. Compliance impacts would only occur if the vulnerability enabled unauthorized data access or processing, which is not indicated in the provided context.

Mitigation Strategies

Update SumatraPDF to the latest patched version that addresses the integer overflow in BuildPageLabelRec(). If using mupdf-based viewers, ensure they include the fix for CVE-2026-88361. Avoid opening untrusted PDFs, especially those with PageLabels /Nums keys. Implement network-level controls to block or quarantine suspicious PDF files.

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