CVE-2026-52886 in Notepad++
Summary
by MITRE • 08/17/2026
Notepad++ is a free and open-source source code editor. Prior to 8.9.7, Notepad++ validates the backupFilePath attribute from session.xml with std::wstring::starts_with against the expected backup directory without path normalization, allowing parent-directory sequences during snapshot-mode restoration to read an arbitrary user-readable file outside the backup directory into an editor tab. This issue is fixed in version 8.9.7.
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Analysis
by VulDB Data Team • 08/17/2026
Notepad++ is a widely used free and open-source source code editor that supports multiple programming languages through plugins and built-in syntax highlighting features. The application maintains user sessions by storing configuration data, including recently opened files and workspace layouts, in an XML-based session file named session.xml. This mechanism allows users to resume their work environment after restarting the application or recovering from a crash. However, prior to version 8.9.7, the implementation of this feature contained a critical path traversal vulnerability that could be exploited during snapshot-mode restoration processes.
The core technical flaw lies in how Notepad++ validates the backupFilePath attribute found within the session.xml file before loading it into an editor tab. The application employs the std::wstring::starts_with function to verify whether the provided file path begins with the expected backup directory string. This validation method is fundamentally flawed because it performs a simple prefix check without normalizing the path or resolving relative components such as parent-directory sequences represented by double dots (..). Consequently, an attacker can craft a malicious session.xml file where the backupFilePath attribute contains a sequence like ../../../../etc/passwd on Linux systems or C:\Windows\System32\config\SAM on Windows. Because the string starts with the expected directory prefix due to improper handling of relative path components, the application accepts it as valid and proceeds to load the specified external file into an editor tab for display.
This vulnerability enables a local information disclosure attack vector where arbitrary user-readable files outside the designated backup directory can be read by the Notepad++ process. The operational impact is significant because it allows attackers who have access to modify session.xml or trick users into opening maliciously crafted project files to exfiltrate sensitive data stored on the victim's machine. This could include configuration files, credentials, source code containing secrets, or other personal documents that are not intended for public viewing but remain readable by the user account executing Notepad++. The attack does not require administrative privileges and can be executed simply by convincing a target to open a maliciously constructed file within the application environment.
From a classification perspective, this vulnerability aligns with CWE-22: Improper Limitation of a Pathname to a Restricted Directory, commonly known as path traversal or directory traversal. The failure to normalize paths before validation is a classic example of trusting user-supplied input without proper sanitization. In the context of the MITRE ATT&CK framework, this behavior facilitates data exfiltration through local file access techniques, specifically leveraging application logic flaws rather than exploiting operating system vulnerabilities directly. It represents an insecure direct object reference scenario where the application fails to ensure that accessed objects are within authorized boundaries.
Mitigation for this issue is straightforward and primarily involves upgrading Notepad++ to version 8.9.7 or later, which includes patches addressing the path normalization logic during session restoration. Users should avoid opening session files or project configurations from untrusted sources until they have verified their integrity. Additionally, security best practices suggest implementing strict input validation that resolves relative paths against a base directory before performing any access checks, ensuring that canonicalized paths remain within allowed boundaries regardless of how many parent-directory sequences are present in the input string.