CVE-2026-56705

Executive Summary

CVE-2026-56705 is a critical pre-authentication remote code execution (RCE) vulnerability affecting Adminer versions prior to 5.4.3. The flaw resides in the failure to sanitize the server field before constructing a PDO DSN string, allowing unauthenticated attackers to inject ODBC parameters via semicolons. Successful exploitation enables an attacker to write PHP code to the web root and achieve remote code execution by accessing the generated trace file.

Administrators of any internet-facing Adminer installation running a version below 5.4.3 should treat this as a critical, actively exploitable risk. No public proof-of-concept (PoC), exploit code, or Nuclei template is currently available, but the vulnerability class is well understood and exploitation is straightforward given the attack surface.

Technical Analysis

Adminer is a lightweight, single-file database management tool written in PHP, frequently deployed for managing MySQL, PostgreSQL, SQLite, and other database systems via a web interface. It is commonly found on shared hosting environments, development servers, and administrative panels, often exposed unintentionally to the internet.

The vulnerability is rooted in the application's handling of the server field during the connection setup process. When a user initiates a database connection, Adminer constructs a PDO DSN string that includes the server hostname. The codebase fails to sanitize or validate this input before embedding it into the DSN. Because PDO DSN strings support connection-specific parameters separated by semicolons, an attacker can append arbitrary key-value pairs to the DSN by injecting semicolon-separated parameters into the server field.

The critical injection vector identified in the advisory involves the TraceFile and TraceOn ODBC parameters. These parameters are supported by certain PDO ODBC drivers:

• TraceOn — enables or disables tracing for the ODBC connection. Setting this to 1 activates tracing.
• TraceFile — specifies the file path to which trace output is written.

By injecting these parameters, an attacker can force the database driver to write trace data to a file of their choosing. Critically, if the attacker sets TraceFile to a path within the web root (e.g., a .php file) and embeds PHP code within other injected parameters or the server field itself, the trace mechanism will write that content to the file. When the file is subsequently requested over HTTP, the PHP interpreter executes the embedded code, resulting in remote code execution.

The attack does not require authentication, as the server field is presented on the login form before any credentials are validated. The CVSS score of 9.8 reflects the full remote impact: network access with low complexity, no privileges required, no user interaction, and a total compromise of confidentiality, integrity, and availability.

The vulnerability is classified under CWE-73 (External Control of File Name or Path), which encompasses the ability to control the file path used in a write operation. In this case, the controlled path is the TraceFile parameter influencing where the application writes data.

It is important to note that insufficient technical detail is available in the advisory to specify the exact code location or function names involved; the description is the authoritative source.

Exploitation Scenarios

No public PoC or exploit code has been released as of this report. The following attack chain is inferred from the vulnerability class and the technical description.

Step 1: Reconnaissance and Target Identification An attacker first identifies internet-facing Adminer instances. This can be done via search engines such as Shodan or Google using dorks like title:Adminer, or by scanning for common Adminer deployment paths (e.g., /adminer.php, /adminer/index.php). Since Adminer is a single-file application, it can be deployed under any filename, making direct fingerprinting partially dependent on content inspection.

Step 2: Triggering the Flaw The attacker navigates to the Adminer login page, which presents a system selection drop-down and a server input field. The attacker can skip any valid database credentials and instead focus on the server field. The attacker submits a request — typically an HTTP POST to the login form — with a crafted server value containing semicolon-separated ODBC parameters.

Step 3: Payload and Execution The attacker constructs a payload resembling the following logic (at the vulnerability-class level):

• Set the server field to a value that includes a valid hostname followed by ;TraceOn=1;TraceFile=/path/to/webroot/shell.php.
• Inject PHP code into another field that becomes part of the trace output. The exact mechanism for embedding the PHP code may vary, but any parameter that gets written to the trace file can carry the payload.

When the connection is attempted, PDO interprets the semicolon-separated parameters, enables tracing, and writes trace output — including the injected PHP code — to the specified file. The attacker then issues a simple HTTP GET request to the written file (e.g., /shell.php). The PHP code executes in the context of the web server, providing a web shell or arbitrary command execution.

Step 4: Post-Exploitation Impact With remote code execution, the attacker gains full control of the web application's runtime environment. Typical post-exploitation activities include:

• Extracting database credentials from the Adminer configuration or environment.
• Reading sensitive files in the web root or system directories.
• Pivoting laterally to internal network segments if the web server has additional connectivity.
• Establishing persistence through web shells, backdoor accounts, or scheduled tasks.
• Encrypting data for ransomware or exfiltrating sensitive records.

The blast radius is limited by the permissions of the web server process, but in many shared or misconfigured environments this equates to full server compromise.

Impact Assessment

The CVSS v3.1 score of 9.8 places this vulnerability in the critical severity range. The vector string AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H reflects:

• Attack Vector (AV): Network — exploitable remotely over the network.
• Attack Complexity (AC): Low — no special conditions beyond network access.
• Privileges Required (PR): None — no authentication needed.
• User Interaction (UI): None — the victim is not required to perform any action.
• Scope (S): Unchanged — the compromise is confined to the affected component.
• Confidentiality, Integrity, Availability (CIA): High — full compromise of all three security properties.

The business impact depends on the environment in which Adminer is deployed. For internet-facing installations, the risk is immediate and severe. For internally-hosted instances, the risk is still significant if the network is not adequately segmented. The infected file written to the web root can serve as a persistent backdoor, surviving reboots and potentially evading detection if not actively monitored.

Media and communications systems that host database management tools are common targets. In a typical scenario, the attacker can pivot from the web shell to the backend database, exfiltrating customer records, financial data, or intellectual property.

Detection Guidance

Sigma Rule

title: Adminer RCE via ODBC Trace File Injection
id: 5c1d4a2e-9f73-4d12-b8e5-7c3a1b9c2d4f
status: experimental
description: Detects HTTP requests to Adminer with injected ODBC trace parameters in the server field
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-56705
author: Valtersit Threat Intel
date: 2026/05/01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - 'TraceOn'
            - 'TraceFile'
        cs-uri-stem|endswith:
            - 'adminer.php'
            - 'adminer/index.php'
            - '.php'
    condition: selection
falsepositives:
    - Legitimate use of ODBC tracing in rare debugging scenarios
level: high

YARA Rule

rule Adminer_ODBC_Trace_Injection {
    meta:
        author = "Valtersit Threat Intel"
        description = "Detects payloads attempting to exploit CVE-2026-56705 via trace file injection"
        cve = "CVE-2026-56705"
        date = "2026-05-01"
        severity = "critical"

    strings:
        $s1 = "TraceOn" ascii wide nocase
        $s2 = "TraceFile" ascii wide nocase
        $s3 = "server=" ascii wide nocase
        $s4 = "<?php" ascii wide nocase
        $s5 = ".php" ascii wide nocase

    condition:
        ($s1 and $s2) and ($s3 or $s5) and filesize < 10KB
}

Suricata IDS Rule

alert http any any -> any any (
    msg:"CVE-2026-56705 Adminer ODBC Trace File Injection Attempt";
    flow:established,to_server;
    http.method; content:"POST";
    http.uri; content:"adminer"; nocase;
    content:"TraceOn"; http.client_body; nocase;
    content:"TraceFile"; http.client_body; nocase;
    pcre:"/(?:TraceOn|TraceFile)=[^;]*(?:;|$)/i";
    classtype:attempted-admin;
    reference:cve,2026-56705;
    sid:10000123;
    rev:1;
)

Elastic Detection

sequence
  by process.entity_id
  [network where process.name == "httpd" or process.name == "nginx" and destination.port == 80]
  [file where event.action == "create" and file.name == "*.php"
     and file.path like "*webroot*" and process.name in ("httpd", "nginx")]

Splunk SPL Query

index=web sourcetype=access_combined
| search "POST" AND ("adminer.php" OR "adminer/index.php")
| regex _raw="(?i)(TraceOn|TraceFile)"
| table _time, src_ip, uri, uri_query, http_user_agent
| sort - _time

Wazuh OSSEC Rule

<rule id="100123" level="15">
    <if_sid>31100</if_sid>
    <regex>(?i)TraceOn|TraceFile</regex>
    <match>adminer</match>
    <description>Possible CVE-2026-56705 Adminer ODBC trace injection exploitation attempt</description>
    <group>web_application_attack,rce,adminer,</group>
    <mitre>
        <id>T1190</id>
    </mitre>
</rule>

Mitigation & Patch Guidance

Patch Status: As of this writing, there is no public patch available beyond upgrading to Adminer 5.4.3 or later. The vendor has not released a formal advisory, and no official mitigation has been documented. The following recommendations should be applied as appropriate.

1. Immediate Mitigations

   • Upgrade to Adminer 5.4.3 or the latest available version immediately. Verify the installed version by checking the application's version string or file metadata.
   • If an immediate upgrade is not possible, restrict network access to Adminer by placing it behind a firewall rule that only permits access from trusted IP ranges or a VPN.
   • Implement a Web Application Firewall (WAF) rule to block HTTP POST requests containing TraceOn or TraceFile parameters in the request body.
   • Disable database management functionality in production environments entirely; remove Adminer from publicly accessible web servers.

2. Patch/Upgrade Steps

   • Identify all servers hosting Adminer via asset inventory or filesystem search for adminer*.php.
   • Download the latest version from the official Adminer website (adminer.org) and replace the existing file.
   • After upgrading, verify that the login page no longer accepts semicolon-injected parameters in the server field.
   • Test all database connections to ensure functionality is not degraded.

3. Long-Term Hardening

   • Restrict Adminer access to administrative networks only; never expose it directly to the internet.
   • Enforce multi-factor authentication on any administrative interface that remains accessible.
   • Monitor web server logs for abnormal POST requests or unexpected .php file creations in the web root.
   • Implement file integrity monitoring on the web root to detect unauthorized file writes.
   • Conduct a review of all public-facing web applications and remove unused management tools.

References

1. NVD — CVE-2026-56705: https://nvd.nist.gov/vuln/detail/CVE-2026-56705 (CVSS 9.8, CWE-73)
2. Adminer Official Site — https://www.adminer.org/ (Latest version: 5.4.3)
3. MITRE ATT&CK — T1190: Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
4. CWE-73 — External Control of File Name or Path: https://cwe.mitre.org/data/definitions/73.html

Threat Actor Campaigns: As of this report date, there are no known active exploitation campaigns or verified exploit-in-the-wild evidence for CVE-2026-56705. The vulnerability class (unauthenticated RCE via parameter injection in admin tools) has been exploited across other products in the past, and this CVE should be considered a high-priority exposure for any organization running affected versions.