CVE-2026-1126 is a security vulnerability identified in the lwj flow product, specifically in the uploadFile function located in the file FormResource.java within the SVG File Handler component. The vulnerability arises from improper validation or restrictions on the File argument, enabling an attacker to upload arbitrary files without restrictions. This unrestricted upload can be exploited remotely without requiring user interaction or elevated privileges beyond low-level access. The vulnerability impacts confidentiality, integrity, and availability by potentially allowing attackers to upload malicious files such as web shells, malware, or unauthorized content, which could lead to further system compromise or data leakage. The product follows a rolling release strategy, which means continuous updates without fixed version numbers, making it difficult to pinpoint affected or patched versions. The vendor has been notified but has not yet issued a fix or response. The CVSS 4.0 score of 5.3 reflects a medium severity, considering the ease of exploitation (network vector, low complexity, no privileges required), but limited scope and impact. No known exploits are currently active in the wild, but public disclosure increases the likelihood of exploitation attempts. The vulnerability is significant for environments where lwj flow is deployed, especially if exposed to untrusted networks.

For European organizations, the unrestricted file upload vulnerability in lwj flow poses risks including unauthorized code execution, data breaches, and service disruption. Attackers could upload malicious payloads leading to server compromise, lateral movement, or defacement. Confidentiality could be impacted if sensitive files are accessed or exfiltrated. Integrity risks arise from unauthorized modification or replacement of legitimate files. Availability could be affected if attackers upload files that disrupt service or consume resources. Organizations using lwj flow in critical infrastructure, government, finance, or healthcare sectors in Europe may face regulatory and reputational damage if exploited. The rolling release nature complicates patch management, increasing exposure time. Remote exploitation without user interaction means attackers can operate stealthily, increasing risk for internet-facing deployments. Although no active exploits are known, the public disclosure and medium severity warrant proactive defense measures.

European organizations should immediately audit their use of lwj flow and identify any exposed instances of the uploadFile functionality. Network segmentation and restricting access to the flow application to trusted internal networks can reduce exposure. Implement strict input validation and file type restrictions at the application or web server level to block unauthorized file types. Employ web application firewalls (WAFs) with rules targeting file upload anomalies. Monitor logs for unusual upload activity or unexpected file types. Since the vendor has not released a patch, consider deploying virtual patching or compensating controls such as disabling file upload features if not essential. Regularly update the software as new releases become available and verify if the vulnerability has been addressed. Conduct penetration testing focused on file upload vectors. Educate administrators on the risks and signs of exploitation. Finally, maintain incident response readiness to quickly contain any compromise resulting from this vulnerability.