Summary: A Broken Access Control vulnerability (CVE-2025-11627) affecting the “Site Checkup — AI Troubleshooting with Wizard and Tips for Each Issue” plugin up to and including version 1.47 allows unauthenticated attackers to poison server-side log files. The vendor released a fixed version 1.48. This post explains the technical risk, how attackers abuse the flaw, practical detection and mitigation steps you can apply immediately (including virtual patching/WAF rules), developer fixes, and an incident response checklist. Written from the perspective of an experienced WordPress security practitioner based in Hong Kong.

Table of contents

• Executive summary
• What “log file poisoning” means and why it matters
• What we know about CVE-2025-11627 (impact and exploitability)
• Indicators of compromise (IoCs) and how to detect exploitation
• Immediate site-owner actions (step-by-step)
• Virtual patch (WAF) rules you can deploy now — examples and explanations
• Sample ModSecurity rules and signature patterns
• Developer guidance — secure coding fixes for plugin authors
• Post-incident hardening and long-term mitigation
• Recovering from a compromise — incident response checklist
• If you need assistance
• Closing notes and resources

Executive summary

The Site Checkup plugin exposed an unauthenticated endpoint that writes user-supplied content to server-side logs without sufficient validation or authorization. Attackers can inject arbitrary content into those logs; when logs are stored in web-accessible or interpretable locations this can be chained to remote code execution (RCE) via LFI or misconfiguration. The issue is classified as Broken Access Control (OWASP A5) and is tracked as CVE-2025-11627.

Immediate risk to site owners:

• Unauthenticated actors can write attacker-controlled data to files the webserver can read.
• Depending on hosting, file locations and other components, this can lead to RCE, full site compromise, data theft, SEO spam or persistent backdoors.
• The vendor released a patch in version 1.48. If you run version 1.47 or earlier, update immediately. If you cannot update now, follow the mitigations below.

What “log file poisoning” means and why it matters

Log file poisoning occurs when untrusted input is written into server-side logs (application logs, debug logs, access logs, or plugin-specific logs). If the attacker can inject executable content (for PHP: <?php ... ?>) into a file that is later interpreted by PHP via inclusion or is directly web-accessible, that becomes an execution vector.

Common exploitation chains:

1. Write PHP into a log file stored inside a web-accessible directory.
2. Trigger a local file inclusion (LFI) or other component that includes the log contents.
3. Execute the injected PHP to gain a shell, add backdoors, or escalate privileges.

Even without direct RCE, poisoned logs are useful for persistence, SEO spam, and evasion. Because CVE-2025-11627 is unauthenticated, the attack surface is the entire internet.

What we know about CVE-2025-11627 — impact and exploitability

• Type: Broken Access Control — unauthenticated log file poisoning
• Affected versions: ≤ 1.47
• Fixed in: 1.48
• CVE: CVE-2025-11627
• Reported: 2025-10-30
• Privileges: Unauthenticated
• CVSS (reported): 6.5 (Medium)

Technical summary (high level): the plugin exposes an unauthenticated endpoint that appends or writes input to a log file without validating the path, sanitizing content, or enforcing authorization. The endpoint allows repeated writes by unauthenticated users.

Exploitability considerations: writing into a file is simple for an attacker with access to the endpoint. Converting poisoned logs into RCE usually requires a second vulnerability (LFI, misconfiguration, or another component including the log). Nevertheless, on shared or misconfigured hosts poisoned logs may be directly executable.

Indicators of compromise (IoCs) — what to look for now

Look for suspicious requests and suspicious lines inside logs. Examples:

1) Unusual requests to plugin endpoints

• Any GET/POST calls to plugin paths or REST routes from unknown IPs outside normal traffic.
• Examples (non-exhaustive):
  • /wp-admin/admin-ajax.php?action=site_checkup_*
  • /wp-json/site_checkup/v1/*
  • Query parameters like log, file, content, path, message

2) Log file entries that contain

• PHP open tags: <?php
• Function names used for code execution: eval(, assert(, system(, passthru(, shell_exec(, base64_decode()
• Long base64 blobs
• Arbitrary HTML/JS in places where logs normally contain plain text
• Repeated suspicious messages from the same IP with payload-like content

3) New or modified files with odd timestamps

• Files created in wp-content/uploads/ or plugin log directories with modification times that match suspicious requests.

4) Webshell indicators

• Files or logs containing patterns such as $_REQUEST, preg_replace('/.*/e', eval(base64_decode( or simple backdoor code.

Where to check: plugin log files (filesystem), web server access and error logs, wp-content/uploads and other writable directories, and any database tables the plugin may use to store logs.

Immediate site-owner actions — step-by-step

If you run Site Checkup ≤ 1.47, follow these immediately.

1. Update (preferred)
   Update the plugin to 1.48 or later as soon as possible. Test on staging if available, then update production.
2. If you cannot update immediately, disable the plugin
   Deactivate from Dashboard → Plugins, or rename the plugin folder via SFTP/SSH (e.g. wp-content/plugins/site-checkup → site-checkup.disabled).
3. Apply short-term WAF/blocking rules
   Block requests to plugin endpoints that accept content for logs, and block patterns containing PHP tags or suspicious function names.
4. Restrict file permissions and locations
   Ensure logs are not web-accessible. Move logs outside web root or enforce strict ACLs. Recommended permissions: files 640, directories 750, owner = web server user. Avoid world read/write.
5. Scan for IoCs and backdoors
   Search for <?php in upload directories, plugin directories and logs. Look for recently modified files. Use malware scanners and manual searches for webshell signatures.
6. Rotate credentials and sessions
   Reset admin passwords, database credentials if compromise is suspected, and rotate API keys/tokens. Force logout all users (change salts in wp-config.php or invalidate sessions).
7. Backup
   Take a full backup before major changes, then take a clean backup after remediation.
8. Notify stakeholders and host
   If you suspect compromise, inform your hosting provider — they may help with infra-level detection and containment.

Virtual patch (WAF) rules you can deploy now — strategy

If you cannot update immediately, virtual patching via a WAF is an effective stop-gap. Recommended protections:

• Block unauthenticated requests to plugin endpoints that write logs.
• Block payloads containing PHP tags, dangerous function names or long base64 blobs.
• Block path traversal sequences (../) in file/path parameters.
• Enforce content-type validation where appropriate (e.g., expect JSON).
• Rate-limit suspicious endpoints to slow automated attacks.

Below are sample ModSecurity rules and conceptual rules you can adapt. Always test in detection-only mode first.

Sample ModSecurity rules and signature patterns

Adapt these to your environment and test on staging.

SecRule REQUEST_BODY|ARGS "@rx <\?(php|=)" \
  "id:1001001,phase:2,deny,log,status:403,msg:'Blocked request containing PHP tags (possible log poisoning attempt)'"

SecRule ARGS|REQUEST_BODY "@rx (eval\(|base64_decode\(|system\(|shell_exec\(|passthru\()" \
  "id:1001002,phase:2,deny,log,status:403,msg:'Blocked suspicious PHP function in request (possible code injection)'"

SecRule ARGS_NAMES|ARGS "@rx (file|path|log|filename|target)" \
  "chain,id:1001003,phase:2,deny,log,status:403,msg:'Blocked path traversal parameter in plugin endpoint'"
SecRule ARGS "@rx \.\./" \
  "t:none"

SecRule ARGS|REQUEST_BODY "@rx (?:[A-Za-z0-9+/]{100,}={0,2})" \
  "id:1001004,phase:2,deny,log,status:403,msg:'Blocked long base64 blob in request (possible payload)'"

SecRule REQUEST_URI "@beginsWith /wp-json/site_checkup" \
  "id:1001005,phase:1,deny,log,status:403,msg:'Blocked unauthenticated access to Site Checkup REST route'"

SecAction "id:1001006,phase:1,pass,nolog,initcol:ip=%{REMOTE_ADDR},setvar:ip.req_counter=+1"
SecRule IP:REQ_COUNTER "@gt 20" "id:1001007,phase:1,deny,status:429,log,msg:'Rate limit exceeded for endpoint'"

Important: Deploy incrementally. Start with logging/audit mode, review false positives, then move to deny. Tailor REQUEST_URI checks to the plugin endpoints in your environment.

Developer guidance — how the plugin should be fixed (secure coding)

For plugin authors or maintainers: the fix should combine authorization, validation, path restrictions and safe storage.

1) Add authorization checks

if ( ! current_user_can( 'manage_options' ) ) {
    wp_send_json_error( 'Forbidden', 403 );
}

For REST routes, use permission callbacks:

register_rest_route( 'site-checkup/v1', '/write-log', array(
  'methods'  => 'POST',
  'callback' => 'sc_write_log',
  'permission_callback' => function () {
      return current_user_can( 'manage_options' );
  },
) );

2) Validate and sanitize inputs

$filename = sanitize_file_name( wp_unslash( $_POST['filename'] ?? '' ) );
$content  = wp_kses_post( wp_unslash( $_POST['content'] ?? '' ) ); // or a stricter sanitizer

Reject filenames with .., leading slashes, or absolute paths. Use realpath() checks.

3) Restrict write location and avoid web-accessible directories

$log_dir = WP_CONTENT_DIR . '/site-checkup-logs';
if ( ! file_exists( $log_dir ) ) {
    wp_mkdir_p( $log_dir );
}
$target = $log_dir . '/' . $filename;

$real_base = realpath( $log_dir );
$real_target = realpath( dirname( $target ) ) . '/' . basename( $target );
if ( strpos( $real_target, $real_base ) !== 0 ) {
    wp_die( 'Invalid target path' );
}

4) Avoid writing executable PHP content

$content = str_replace( array('<?php', '<?', '?>'), '', $content );

5) Use the WordPress Filesystem API where appropriate

WP_Filesystem abstracts differences across hosting and can reduce mistakes when writing files.

6) Logging best practices

• Use structured logs (timestamp, sanitized fields).
• Rotate logs and cap sizes.
• Set strict ownership and permissions on log files.

7) Nonce and CSRF protection

if ( ! wp_verify_nonce( $_REQUEST['_wpnonce'] ?? '', 'site_checkup_action' ) ) {
    wp_send_json_error( 'Invalid nonce', 403 );
}

8) Limit user-supplied content length

Reject excessively long payloads and set reasonable caps.

Combining authorization checks, strict sanitization, path validation and safe write locations will eliminate the log poisoning vector.

Post-incident hardening — actions after remediation

• Re-scan the site with a trusted malware scanner.
• Perform file integrity checks against a known-good backup.
• Review server and access logs for evidence of exploitation.
• Remove or sanitize any poisoned logs. If logs contained PHP and were accessible, treat the site as potentially compromised.
• Reset administrative passwords and rotate secrets.
• Harden PHP and webserver configuration (disable execution in upload directories, restrict open_basedir, disable risky PHP functions).
• Set up monitoring and alerting for future plugin vulnerabilities.

Recovering from a compromise — incident response checklist

1. Contain: Take the site offline or maintenance mode. Isolate the host if possible.
2. Preserve evidence: Snapshot files and database for forensics before overwriting.
3. Eradicate: Replace infected files with clean copies, remove unauthorized users and scheduled tasks, and remove suspicious PHP code in logs/uploads.
4. Recover: Restore from a clean backup predating the compromise, re-apply updates and monitor closely.
5. Learn: Conduct root-cause analysis and implement long-term hardening.

If you are not comfortable performing these steps, engage a qualified incident response provider or a security professional.

If you need assistance

If you require help deploying WAF rules, scanning for IoCs, or performing incident response, contact an experienced security consultant or your hosting provider’s security team. Avoid unverified automated services; choose a provider with transparent methodology and references.

Final notes and practical reminders

• Update the plugin to version 1.48 or later immediately. This is the most effective remediation.
• If you cannot apply the vendor fix, disable the plugin and apply conservative WAF rules blocking PHP tags, known dangerous functions and path traversal attempts.
• Treat signs of log poisoning seriously — it commonly precedes more extensive compromise.
• For developers: enforce permissions, sanitize all inputs, avoid writing untrusted input to web-accessible paths, and follow WordPress secure coding standards.
• Keep backups and enable logging — they are essential for recovery and investigation.