CVE-2026-107225 in excelize
Summary
by MITRE • 10/07/2026
Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.8.0 to 2.11.0, GetStyle's fill, border, and font extraction predicates check only upper bounds for attacker-controlled style-table indices. File.GetStyle relies on extractStyleCondFuncs predicates that allow negative FillID, BorderID, and FontID values to reach slice indexing. When a crafted styles.xml supplies a negative fillId, borderId, or fontId and the application reads the style, a negative identifier passes the upper-bound-only predicate and becomes a negative slice index, allowing an attacker to panic while reading cell styling. No fixed version is available as of this review.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in Excelize versions 2.8.0 through 2.11.0 represents a critical input validation failure within the Go language library responsible for processing Microsoft Excel spreadsheet files. This specific flaw resides in the GetStyle function, which is tasked with extracting styling information such as fill patterns, borders, and font attributes from the underlying XML structure of an Excel file. The core technical deficiency lies in how the extractStyleCondFuncs predicates handle index validation when accessing internal style tables. Specifically, these predicates perform checks exclusively against upper bounds for attacker-controlled indices representing FillID, BorderID, and FontID values. This incomplete validation logic fails to account for negative integer inputs, creating a significant gap in security controls that allows maliciously crafted data to bypass standard safety mechanisms designed to prevent out-of-bounds access.
When an application utilizing the affected versions of Excelize processes a specially constructed styles.xml file containing negative identifiers for fill, border, or font attributes, the validation logic incorrectly deems these values as valid because they do not exceed the defined upper limits. Consequently, these negative integer values are passed directly to slice indexing operations within the Go runtime environment. In Go, accessing an array or slice with a negative index is undefined behavior that typically results in a panic condition rather than returning an error code or handling the exception gracefully. This mechanism allows an attacker who can influence the content of Excel files processed by the application to trigger a denial-of-service attack against any service relying on this library for file parsing, such as web applications accepting user-uploaded spreadsheets or automated data processing pipelines.
The operational impact of this vulnerability is primarily centered around availability and system stability. By forcing the Go runtime into a panic state, an attacker can cause immediate application crashes, leading to service interruptions. In environments where Excelize is used within long-running processes or web servers without robust external crash recovery mechanisms, repeated exploitation could lead to sustained downtime. Furthermore, depending on how the surrounding application handles panics, there may be secondary risks related to information disclosure if stack traces are exposed to end-users during error handling phases. The lack of a fixed version as of this review exacerbates the risk profile for organizations dependent on this library, necessitating immediate defensive coding practices or temporary workarounds such as input sanitization at the application layer before passing data to Excelize functions.
From a classification perspective, this vulnerability aligns with CWE-129, which describes improper validation of array index values, specifically highlighting the failure to validate for negative indices in contexts where only upper bounds are checked. It also relates closely to CWE-787, as it involves an out-of-bounds write or read scenario that leads to a crash rather than arbitrary code execution due to language-specific memory safety guarantees in Go. In terms of adversarial tactics, this exploit vector corresponds to the ATT&CK technique T1499, Endpoint Denial of Service, where attackers leverage software vulnerabilities to disrupt normal operations by causing application crashes or resource exhaustion. Mitigation strategies should focus on implementing strict input validation that checks for both lower and upper bounds before any slice indexing occurs, ensuring that all style identifiers are non-negative integers within the expected range defined by the Excel specification standards.