The vulnerability CVE-2026-24486 affects the python-multipart library, a streaming multipart parser used in Python applications to handle file uploads. Specifically, the flaw is a path traversal vulnerability (CWE-22) that exists when the library is configured with UPLOAD_KEEP_FILENAME set to True and a non-default UPLOAD_DIR. Under these conditions, an attacker can craft a malicious filename in the multipart upload request that includes path traversal sequences (e.g., '../') to escape the intended upload directory and write files to arbitrary locations on the server's filesystem. This can lead to unauthorized file creation or overwriting, potentially compromising the integrity of the system and enabling further attacks such as remote code execution or denial of service. The vulnerability does not require any authentication or user interaction, and it can be exploited remotely over the network. The CVSS v3.1 score of 8.6 reflects the high impact on integrity and moderate impact on availability, with low attack complexity and no privileges required. The vulnerability was patched in version 0.0.22 of python-multipart, and users are advised to upgrade to this version or later. Alternatively, disabling the UPLOAD_KEEP_FILENAME option mitigates the risk by preventing the use of attacker-controlled filenames. No public exploits have been reported yet, but the potential impact warrants immediate attention.

For European organizations, this vulnerability poses a significant risk especially to web applications and APIs that utilize python-multipart for handling file uploads. Successful exploitation can lead to arbitrary file writes outside the intended directories, potentially allowing attackers to overwrite critical system files, deploy web shells, or manipulate application data. This threatens the confidentiality and integrity of sensitive data and can disrupt service availability. Organizations in sectors such as finance, healthcare, and government, which often handle sensitive personal and operational data, face heightened risks. Additionally, the ease of exploitation without authentication increases the attack surface, making automated attacks feasible. The impact is exacerbated in environments where python-multipart is used in production without strict input validation or sandboxing. Given the widespread adoption of Python in European software development, the vulnerability could affect a broad range of organizations if unpatched.

1. Upgrade python-multipart to version 0.0.22 or later immediately to apply the official patch. 2. If upgrading is not immediately feasible, disable the UPLOAD_KEEP_FILENAME configuration option to prevent the use of attacker-controlled filenames. 3. Implement strict input validation and sanitization on filenames before processing uploads to detect and block path traversal sequences. 4. Employ filesystem permissions and sandboxing to restrict the write access of the application process to only necessary directories. 5. Monitor file upload directories and system logs for unusual file creation or modification patterns indicative of exploitation attempts. 6. Conduct code reviews and penetration testing focused on file upload functionality to identify and remediate similar vulnerabilities. 7. Educate developers about secure file handling practices and the risks of path traversal. 8. Use Web Application Firewalls (WAFs) with rules to detect and block path traversal payloads in HTTP requests.