Adminer is an open-source database management tool widely used for managing SQL databases through a web interface. The vulnerability CVE-2026-25892 affects Adminer versions from 4.6.2 up to 5.4.1 and stems from improper input validation (CWE-20) in its version check mechanism. Adminer periodically checks for updates by receiving signed version information via JavaScript postMessage from adminer.org, which the browser then posts to the ?script=version endpoint. This endpoint, however, does not validate the origin of incoming POST requests, accepting data from any source. An attacker can exploit this by sending a crafted POST request with the version[] parameter. PHP automatically converts this parameter into an array rather than the expected string. When Adminer subsequently calls openssl_verify() to verify the signature, it receives an array instead of a string, causing a TypeError exception. This exception results in an HTTP 500 Internal Server Error response, effectively causing a denial-of-service (DoS) condition that affects all users accessing the Adminer instance. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network, making it highly accessible to attackers. Although no known exploits are currently in the wild, the CVSS 3.1 score of 7.5 (high severity) reflects the ease of exploitation and the impact on availability. The fix implemented in Adminer 5.4.2 includes proper origin validation and input sanitization to prevent malicious POST requests from causing this failure. Organizations using vulnerable Adminer versions should upgrade promptly to mitigate this risk.

The primary impact of CVE-2026-25892 is a denial-of-service condition that disrupts the availability of the Adminer database management interface. For European organizations relying on Adminer for database administration, this could result in temporary loss of access to critical database management functions, delaying maintenance, backups, or emergency interventions. This disruption could affect operational continuity, especially in sectors such as finance, healthcare, government, and critical infrastructure where database availability is crucial. Although the vulnerability does not directly compromise confidentiality or integrity, the inability to manage databases effectively could indirectly increase risk exposure. Additionally, the ease of exploitation without authentication or user interaction means attackers can launch DoS attacks at scale, potentially targeting multiple organizations or critical service providers simultaneously. This could lead to cascading effects in interconnected systems and services. The lack of known exploits in the wild suggests limited current impact, but the vulnerability’s characteristics warrant proactive mitigation to prevent future attacks.

1. Immediate upgrade to Adminer version 5.4.2 or later, which contains the patch for this vulnerability. 2. If upgrading is not immediately possible, implement network-level controls such as web application firewalls (WAFs) to restrict access to the ?script=version endpoint, allowing only trusted origins or IP addresses. 3. Monitor web server logs for unusual POST requests to the ?script=version endpoint, particularly those containing the version[] parameter, to detect potential exploitation attempts. 4. Employ strict Content Security Policy (CSP) headers and CORS policies to limit cross-origin requests to Adminer interfaces. 5. Isolate Adminer instances behind VPNs or internal networks to reduce exposure to external attackers. 6. Regularly audit and update all database management tools and related software to ensure timely application of security patches. 7. Educate IT and security teams about this specific vulnerability and the importance of validating input origins in web applications.