CVE-2026-107219 in excelize
Summary
by MITRE • 10/07/2026
Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.3.1 to 2.11.0, agile decryption accepts an attacker-controlled spinCount and performs that many password-key derivation iterations before verifier validation. OpenFile reaches agileDecrypt, which passes the unbounded spinCount to convertPasswdToKey before password verification. When a crafted OLE encrypted-workbook header supplies an excessive spinCount and the file is opened, the key-derivation loop performs unbounded attacker-selected work and cannot be cancelled, allowing an attacker to consume a CPU core for an attacker-controlled duration. 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 the Excelize library, specifically affecting versions from 2.3.1 through 2.11.0, represents a critical resource exhaustion flaw rooted in improper input validation during the decryption process for Microsoft Excel files. Excelize is widely utilized Go language library designed to facilitate reading and writing operations on Microsoft Excel spreadsheets. The core of this issue lies within the agile encryption handling mechanism, which is responsible for deriving cryptographic keys from user-provided passwords. When an application utilizes Excelize to open a file that employs Agile Encryption, the library invokes the OpenFile function, which subsequently calls the agileDecrypt routine. This routine is tasked with processing the encrypted workbook header and validating the provided password against stored verifiers. However, within this workflow, there exists a significant failure in enforcing bounds on critical parameters extracted from the input data.
The technical flaw centers on the spinCount parameter found within the OLE encrypted-workbook header of crafted Excel files. In standard Agile Encryption implementations, such as those defined by Microsoft for Office Open XML formats, the spinCount dictates the number of iterations performed during password-based key derivation functions like PBKDF2 or similar algorithms to strengthen the derived encryption keys against brute-force attacks. While a higher spin count is generally beneficial for security in legitimate scenarios, it also increases computational cost. The vulnerability arises because Excelize fails to validate whether the spinCount value supplied by an attacker-controlled file falls within acceptable limits before passing it to the convertPasswdToKey function. Instead of rejecting excessively large values or capping them at a safe maximum, the library accepts any integer provided in the header and uses it directly as the iteration count for the key derivation loop.
This lack of validation leads to an unbounded execution path where the CPU is forced to perform a massive number of cryptographic iterations determined entirely by the attacker. Because the convertPasswdToKey function executes this loop without interruption or cancellation mechanisms, once triggered, the process consumes computational resources until completion. An attacker can craft a malicious Excel file with a spinCount value set to an extremely high integer, such as several hundred million or more. When a victim opens this file using a vulnerable version of Excelize, the application enters a prolonged state of heavy CPU utilization. The operation cannot be easily aborted by standard means because it is embedded within a blocking cryptographic routine that lacks timeout controls. This results in a Denial of Service condition where one core of the processor is monopolized for an attacker-controlled duration, potentially freezing applications or systems depending on their resource allocation and threading models.
From a classification perspective, this vulnerability aligns with CWE-400: Uncontrolled Resource Consumption, as the application fails to limit the amount of resources consumed during processing. It also relates closely to CWE-770: Allocation of Resources Without Limits or Throttling in Cloud Environments, particularly if Excelize is used within server-side applications that process user-uploaded documents. In terms of attack vectors and tactics, this behavior corresponds to ATT&CK technique T1496: Resource Hijacking, where an attacker uses computing resources for their own purposes without the victim's consent, effectively causing a denial of service by exhausting system capacity. The impact is primarily operational disruption rather than data leakage or remote code execution in this specific context, although prolonged resource exhaustion can lead to secondary failures such as application crashes or timeouts that may disrupt broader services relying on document processing capabilities.
Mitigation strategies for organizations utilizing Excelize must focus on immediate version updates and defensive coding practices until a patched release is officially published by the maintainers. Since no fixed version was available at the time of this review, developers should consider implementing custom wrappers around the OpenFile function to intercept and sanitize input parameters before they reach the core library logic. Specifically, applications should validate that any spinCount or iteration count extracted from encrypted documents does not exceed a predefined threshold, such as 100,000 iterations, which is typically sufficient for security purposes without causing performance degradation. Additionally, integrating timeout mechanisms around file processing operations can help mitigate the impact by terminating long-running cryptographic tasks before they consume excessive CPU time. Monitoring system resources and implementing rate limiting on document upload endpoints can also provide an additional layer of defense against such resource exhaustion attacks. Until a permanent fix is released, treating all encrypted Excel files as untrusted input and applying strict validation rules to encryption metadata parameters remains the most effective temporary countermeasure.