CVE-2026-27641

Comprehensive Technical Analysis of CVE-2026-27641

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2026-27641

Description: Flask-Reuploaded, a library providing file upload functionality for Flask applications, contains a critical path traversal and extension bypass vulnerability. This flaw allows remote attackers to achieve arbitrary file write and remote code execution (RCE) through Server-Side Template Injection (SSTI).

CVSS Score: 9.8

Severity Evaluation: The CVSS score of 9.8 indicates a critical vulnerability. This high score is due to the potential for remote code execution, which can lead to complete system compromise. The vulnerability's impact is severe, affecting confidentiality, integrity, and availability.

2. Potential Attack Vectors and Exploitation Methods

Attack Vectors:

1. Path Traversal: An attacker can manipulate file paths to access or overwrite files outside the intended directory.
2. Extension Bypass: An attacker can bypass file extension checks to upload malicious files.
3. Server-Side Template Injection (SSTI): An attacker can inject malicious code into templates, leading to RCE.

Exploitation Methods:

• File Upload Manipulation: An attacker can upload a file with a crafted name that includes path traversal sequences (e.g., ../../etc/passwd) to overwrite critical system files.
• Template Injection: By injecting malicious code into the file name or content, an attacker can exploit SSTI to execute arbitrary commands on the server.

3. Affected Systems and Software Versions

Affected Software:

• Flask-Reuploaded versions prior to 1.5.0

Affected Systems:

• Any system running a Flask application that uses Flask-Reuploaded for file uploads.

4. Recommended Mitigation Strategies

Immediate Actions:

1. Upgrade: Upgrade Flask-Reuploaded to version 1.5.0 or later, which includes the patch for this vulnerability.
2. Input Validation: Implement strict input validation for file names and content to prevent path traversal and extension bypass.
3. Auto-Generated Filenames: Use auto-generated filenames instead of user-provided names to avoid injection attacks.
4. Template Security: Ensure that templates are securely rendered to prevent SSTI.

Long-Term Strategies:

1. Regular Audits: Conduct regular security audits of all third-party libraries and dependencies.
2. Security Training: Train developers on secure coding practices and common vulnerabilities.
3. Monitoring: Implement monitoring and logging to detect and respond to suspicious file upload activities.

5. Impact on Cybersecurity Landscape

Immediate Impact:

• Organizations using Flask-Reuploaded are at high risk of RCE attacks, which can lead to data breaches, system compromise, and service disruptions.

Long-Term Impact:

• This vulnerability highlights the importance of secure file handling and input validation in web applications.
• It underscores the need for continuous monitoring and timely patching of third-party libraries.

6. Technical Details for Security Professionals

Vulnerability Details:

• Path Traversal: The vulnerability allows attackers to manipulate file paths to access or overwrite files outside the intended directory.
• Extension Bypass: The flaw enables attackers to bypass file extension checks, allowing the upload of malicious files.
• SSTI: The injection of malicious code into templates can lead to RCE, allowing attackers to execute arbitrary commands on the server.

Patch Information:

• The vulnerability has been patched in Flask-Reuploaded version 1.5.0. The patch includes improvements in file handling and input validation to prevent path traversal and SSTI.

References:

• GitHub Commit
• GitHub Pull Request
• GitHub Security Advisory

Conclusion: CVE-2026-27641 is a critical vulnerability that requires immediate attention. Organizations should prioritize upgrading to the patched version of Flask-Reuploaded and implement robust input validation and monitoring practices to mitigate the risk of exploitation. This incident serves as a reminder of the importance of secure coding practices and continuous security assessments in maintaining a robust cybersecurity posture.