CVE-2026-34964 in Adminer
Summary
by MITRE • 08/25/2026
Adminer before 5.5.0 contains a server-side request forgery vulnerability in the login form's server field validator, which only inspects leading integers for privileged ports and fails to reject non-numeric port values. Attackers can inject PDO DSN keys like host= and port= into the server parameter to bypass the privileged-port restriction and establish TCP connections to arbitrary internal hosts and ports before authentication.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability identified in Adminer versions prior to 5.5.0 represents a critical security flaw rooted in insufficient input validation within the application's login interface, specifically targeting the server field validator. This weakness allows for Server-Side Request Forgery attacks by exploiting how the backend processes connection parameters before performing authentication checks. The core technical failure lies in the logic used to restrict access to privileged ports; rather than validating the entire string format of the port number or enforcing strict type checking, the system only inspects leading integers. This partial validation approach creates a significant bypass vector where non-numeric characters appended after valid integer sequences are ignored by the security check but retained and processed by the underlying database connection logic.
From an operational perspective, this flaw enables attackers to manipulate the PHP Data Objects (PDO) DSN string through the server parameter. By injecting specific key-value pairs such as host= or port= directly into the input field, adversaries can override default configuration settings. Because this validation and processing occur before authentication is required, the vulnerability allows for unauthenticated access to internal network resources. An attacker can establish TCP connections to arbitrary hosts and ports within the local network infrastructure, effectively turning Adminer into a pivot point for further lateral movement or data exfiltration from behind firewalls that would otherwise block direct external access to those services.
This issue is classified under CWE-20 as Improper Input Validation, specifically highlighting the failure to enforce strict syntactic constraints on user-supplied input. Furthermore, it aligns with MITRE ATT&CK technique T1190, Exploit Public-Facing Application, where attackers leverage vulnerabilities in internet-facing software to gain initial access or execute commands within a trusted network environment. The ability to bypass authentication by manipulating connection parameters before the login process completes makes this particularly dangerous for applications deployed in DMZs or public cloud environments.
Mitigation strategies must prioritize immediate patching to version 5.5.0 or later, where the input validation logic has been corrected to enforce strict type checking and reject non-numeric port values entirely. In cases where upgrading is not immediately feasible, network-level controls such as Web Application Firewalls should be configured to detect and block requests containing suspicious PDO DSN injection patterns in server parameters. Additionally, administrators should ensure that Adminer instances are placed behind robust authentication gateways or restricted access lists to minimize the attack surface exposed to unauthenticated users until the software is updated.