CVE-2025-43960: Adminer DoS Vulnerability via Payload

CVE-2025-43960 Overview

CVE-2025-43960 affects Adminer 4.8.1, a popular PHP-based database management tool, when it uses the Monolog logging library. The vulnerability allows remote, unauthenticated attackers to trigger a Denial of Service (DoS) by submitting a crafted serialized payload. The payload abuses PHP's unserialize() behavior to allocate excessive memory, leading to PHP Object Injection and resource exhaustion [CWE-502]. A single malicious request can render the Adminer interface unresponsive, and concurrent requests can crash the host process entirely.

Critical Impact

Remote unauthenticated attackers can exhaust server memory and crash Adminer-hosted services without authentication or user interaction.

Affected Products

• Adminer 4.8.1
• Adminer deployments configured with Monolog as the logging backend
• PHP applications bundling the affected Adminer release

Discovery Timeline

• 2025-08-25 - CVE-2025-43960 published to NVD
• 2025-09-12 - Last updated in NVD database

Technical Details for CVE-2025-43960

Vulnerability Analysis

The flaw resides in how Adminer 4.8.1 processes serialized PHP data when Monolog is used for logging. PHP's unserialize() function recreates objects from string representations and honors length declarations embedded in the payload. An attacker can submit a serialized string such as s:1000000000:"..." that instructs the parser to allocate roughly one gigabyte of memory.

Because Adminer accepts and routes the data into the deserialization path before any sanity check on size, the PHP worker attempts to honor the allocation. The process either exhausts the PHP memory_limit and aborts, or saturates server RAM. Multiple concurrent requests amplify the effect and can require manual intervention to restore service.

Root Cause

The root cause is unsafe deserialization of attacker-controlled input combined with the absence of size or type validation prior to invoking unserialize(). The issue maps to [CWE-502] Deserialization of Untrusted Data. Monolog's serialization handling within the affected Adminer release expands the attack surface by introducing object instantiation paths reachable from unauthenticated requests.

Attack Vector

Exploitation is network-based and requires no privileges or user interaction. An attacker sends an HTTP request containing a crafted serialized object to the Adminer endpoint. The server parses the payload, triggers the inflated memory allocation, and either hangs or terminates the worker. Repeating the request in parallel produces a server-level DoS.

No public proof-of-concept exploit is listed in CISA KEV, and the vulnerability is not flagged as known-exploited. Technical references are available in the GitHub CVE-2025-43960 details repository and the Adminer v4.8.1 to v4.8.2 diff.

Detection Methods for CVE-2025-43960

Indicators of Compromise

• HTTP POST requests to Adminer endpoints containing serialized PHP markers such as O:, a:, or s: followed by unusually large integer length declarations.
• PHP error log entries reporting Allowed memory size of N bytes exhausted originating from the Adminer process.
• Sudden spikes in resident memory usage on web servers hosting Adminer, followed by worker crashes.
• Web server returning HTTP 500 or connection-reset errors from /adminer.php under low traffic conditions.

Detection Strategies

• Inspect request bodies for serialized payloads exceeding a reasonable size threshold (for example, length values greater than 10 MB).
• Correlate Adminer access logs with PHP-FPM worker restarts and out-of-memory kernel events.
• Apply Web Application Firewall (WAF) signatures that flag PHP serialized strings with oversized s: length specifiers in untrusted parameters.

Monitoring Recommendations

• Monitor process memory ceilings and PHP memory_limit violations on hosts running Adminer.
• Alert on repeated 5xx responses or worker restarts from the Adminer virtual host within short time windows.
• Enable verbose logging on Monolog handlers and forward records to a central SIEM for anomaly review.

How to Mitigate CVE-2025-43960

Immediate Actions Required

• Upgrade Adminer to version 4.8.2 or later, which contains the upstream fix referenced in the v4.8.1 to v4.8.2 comparison.
• Restrict access to Adminer using IP allow-lists, VPN, or HTTP authentication so the endpoint is not exposed to the public internet.
• Lower the PHP memory_limit for the Adminer virtual host to constrain the impact of any single request.

Patch Information

The Adminer maintainers addressed the issue in release 4.8.2. Review the upstream changes at the Adminer GitHub repository and obtain the official build from the Adminer project site. Operators bundling Adminer inside other applications should rebuild and redeploy with the patched version.

Workarounds

• Disable Monolog-based logging in Adminer until the upgrade is complete.
• Deploy a WAF rule that rejects request bodies containing PHP serialized strings with s: length values above a safe threshold.
• Place Adminer behind authentication at the reverse-proxy layer so unauthenticated requests cannot reach the vulnerable handler.
• Run Adminer in a resource-constrained container with strict memory limits to contain DoS attempts.

# Configuration example: constrain PHP memory and reject oversized request bodies in nginx
# /etc/php/8.x/fpm/pool.d/adminer.conf
php_admin_value[memory_limit] = 128M

# /etc/nginx/conf.d/adminer.conf
server {
    listen 443 ssl;
    server_name adminer.internal.example;

    client_max_body_size 1m;

    location / {
        allow 10.0.0.0/8;
        deny all;
        auth_basic "Adminer";
        auth_basic_user_file /etc/nginx/.htpasswd;
        include fastcgi_params;
        fastcgi_pass unix:/run/php/adminer.sock;
    }
}