CVE-2026-107053 in Librera PDF Reader
Summary
by MITRE • 10/29/2026
Insecure permissions in foobnix Librera PDF Reader versionCode 7222 allows unauthorized attackers to arbitrarily write and truncate files in a shared storage space outside of the sandbox.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in foobnix Librera PDF Reader, specifically within application version code 7222, represents a critical failure in access control mechanisms governing file system interactions on Android devices. This flaw is categorized under CWE-732 as improper permission assignment for sensitive resources, indicating that the application has been configured with overly permissive security attributes regarding its interaction with external storage environments. In modern mobile operating systems like Android, applications are typically confined to a sandboxed environment where they can only read and write data within their designated private directories unless explicit permissions are granted by the user or system for broader access. However, in this instance, the application has been configured to operate with elevated privileges that allow it to bypass these standard isolation boundaries without sufficient validation of intent or context.
The technical core of this vulnerability lies in how the application handles file operations on shared storage spaces such as external SD cards or public directories like Downloads and Documents. Instead of restricting write access strictly to files created by the app itself, the insecure permissions allow any process with similar privileges, or potentially malicious actors who have gained a foothold within the device's ecosystem, to arbitrarily target existing files. This capability includes not only writing new data but also truncating existing files, which effectively erases their content while preserving the file structure. Such behavior deviates significantly from secure coding practices that mandate strict adherence to least privilege principles and explicit ownership verification before performing destructive operations on shared resources.
From an operational perspective, this vulnerability poses severe risks to user privacy and data integrity. An attacker who can exploit these insecure permissions could overwrite critical configuration files belonging to other applications or users, leading to application crashes or misconfigurations that degrade device functionality. More critically, the ability to truncate files means that important documents, such as personal PDFs stored in shared directories for easy access by Librera, can be instantly corrupted and rendered unreadable without any warning mechanism. This constitutes a denial of service against specific data assets and undermines trust in the application's reliability. Furthermore, if an attacker gains initial access through another vector, this permission flaw provides a lateral movement opportunity to escalate privileges or persist within the system by modifying shared libraries or scripts that rely on predictable file states.
This behavior aligns with several techniques observed in mobile threat landscapes as documented in the MITRE ATT&CK framework for Android, particularly those related to resource hijacking and data manipulation. The lack of proper validation before writing to external storage mirrors patterns seen in malware families designed to sabotage user data or disrupt service availability on compromised devices. By allowing arbitrary write and truncate operations outside the sandbox, the application creates a persistent attack surface that remains exploitable even if other security controls are strengthened, as it relies fundamentally on flawed file system permissions rather than complex logic errors.
To mitigate this vulnerability, developers must immediately audit all file I/O operations within the Librera PDF Reader codebase to ensure they adhere strictly to Android's scoped storage guidelines introduced in API level 29 and enforced more rigorously in subsequent versions. Applications should avoid using legacy external storage paths for critical data unless absolutely necessary and instead utilize private app-specific directories which are automatically sandboxed. If shared access is required, the application must implement explicit checks to verify file ownership before performing write or truncate operations, ensuring that only files created by the application itself can be modified in this manner. Additionally, utilizing Content Providers with strict URI permissions can help restrict data exposure to authorized components only. Users affected by this issue should update to a patched version as soon as it is released and consider revoking unnecessary storage permissions for applications that do not require broad file system access until remediation occurs.