CVE-2025-10929 is a vulnerability classified under CWE-1288, which pertains to improper validation of consistency within input data. Specifically, this issue affects the Drupal Reverse Proxy Header component versions before 1.1.2, including version 0.0.0. The vulnerability arises because the component fails to properly validate the consistency of user-controlled input within HTTP headers forwarded by reverse proxies. Reverse proxy headers are commonly used to convey client information such as IP addresses or protocol details to backend servers. Improper validation can allow an attacker to manipulate these headers, potentially causing the application to misinterpret client information or behave unexpectedly. According to the CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L), the vulnerability is remotely exploitable over the network without authentication or user interaction, with low attack complexity. The impact is limited to availability, meaning the attacker could cause denial of service or disrupt normal operations but cannot access or modify data. No known exploits have been reported in the wild, and no patches are linked yet, but upgrading to version 1.1.2 or later is recommended once available. This vulnerability is significant for Drupal deployments behind reverse proxies, which are common in modern web hosting environments. Attackers could exploit this flaw to disrupt services or cause instability in web applications relying on Drupal's reverse proxy header processing.

For European organizations, the impact of CVE-2025-10929 primarily concerns availability disruptions in web applications using Drupal behind reverse proxies. Many European enterprises, government agencies, and service providers rely on Drupal for content management and web presence. Exploitation could lead to denial of service conditions or erratic application behavior, potentially affecting business continuity and user experience. Although confidentiality and integrity are not directly impacted, availability issues can cause operational downtime, loss of customer trust, and financial consequences. Organizations with critical public-facing websites or services using reverse proxy headers are particularly vulnerable. The lack of required authentication and ease of remote exploitation increase the risk of opportunistic attacks. However, the absence of known exploits in the wild and the medium CVSS score suggest the threat is moderate but should not be ignored. Proactive patching and input validation are essential to mitigate potential disruptions.

1. Upgrade the Drupal Reverse Proxy Header component to version 1.1.2 or later as soon as the patch is available to address the vulnerability directly. 2. Implement strict validation and sanitization of HTTP headers at the reverse proxy or load balancer level to prevent malicious or malformed headers from reaching the backend Drupal application. 3. Configure web application firewalls (WAFs) to detect and block suspicious header manipulations related to reverse proxy headers. 4. Monitor web server and application logs for unusual patterns in header values or repeated access attempts that could indicate exploitation attempts. 5. Conduct regular security assessments and penetration testing focusing on reverse proxy configurations and header handling. 6. Educate system administrators and developers about the risks of improper header validation and enforce secure coding practices. 7. If immediate patching is not possible, consider temporarily disabling or restricting reverse proxy header processing features until a fix is applied. 8. Maintain an incident response plan to quickly address any availability issues arising from exploitation attempts.