CVE-2026-1557: Unauthenticated Path Traversal → Arbitrary File Download in WP Responsive Images (<= 1.0)

Date: 26 Feb, 2026  |  Severity: High (CVSS 7.5)  |  Affected versions: WP Responsive Images ≤ 1.0

Author: Hong Kong security expert — urgent operational advisory for site owners and developers handling WordPress installations.

A recently disclosed vulnerability in the “WP Responsive Images” plugin (versions up to 1.0) allows an unauthenticated attacker to use a path traversal vector in the plugin’s handling of an image src parameter to read arbitrary files from a WordPress site. This can expose sensitive files such as wp-config.php, backups, private uploads, and other configuration files.

Executive summary (what you need to know now)

• What it is: An unauthenticated path traversal vulnerability in the plugin code that processes an image src parameter, allowing traversal like ../../ to fetch files outside the intended directory.
• What’s at stake: Arbitrary file download. Exposed files may include database credentials, backups, .env files, private keys, and other secrets.
• Ease of exploitation: High — no authentication required, simple payloads, attractive to automated scanners and mass exploitation.
• Immediate action: If the plugin is present, disable or remove it until a patched release is available. Block traversal-style requests at the perimeter, harden file permissions, and remove sensitive files from public web directories.
• If exploited: Treat as a breach: preserve logs, rotate credentials, perform a full forensic and malware inspection, and restore from known-clean backups where necessary.

How the vulnerability works (technical but concise)

The plugin accepts a src parameter and uses it to read and return files from disk. If that input isn’t properly canonicalized and validated, concatenating the value with a base path allows an attacker to use traversal sequences (for example, ../ or encoded variants like %2e%2e%2f) to escape the intended directory and access arbitrary files accessible to the web server user.

Why this is dangerous:

• The webserver process often has read access to files that contain secrets (e.g., wp-config.php, exported SQL files).
• Attackers can mass-scan for this exact pattern and script exploitation across many sites.
• Obtained file contents can be used to escalate: database credentials, API tokens, or keys can lead to further compromise.

No proof-of-concept payloads are published here to avoid enabling abuse. The remainder of this advisory focuses on detection, mitigation, and secure fixes.

Affected components and typical request patterns

Affected: plugin endpoints that accept an image src (query string or form field) and serve files.

Watch for suspicious requests in access logs, for example:

• Requests containing src=../../ or src=%2e%2e%2f.
• Requests attempting to fetch wp-config.php, database.sql, .env, id_rsa, or /etc/passwd.
• Requests to plugin PHP endpoints with long traversal sequences or multiple encodings.

Indicators:

• 200 responses for plugin endpoints that shouldn’t return file content.
• Unusual response sizes or unexpected content types (e.g., text/plain for a .php file).
• Repeated requests from same IPs trying different sensitive filenames.

Real-world impact scenarios

1. Disclosure of database credentials: Extracting wp-config.php can reveal DB credentials and enable data exfiltration or manipulation.
2. Exposure of backups: Backups in webroot can be stolen, providing full site content and database dumps.
3. Discovery of API keys or tokens: Stolen tokens may be abused against external services.
4. Chained attacks: File disclosure combined with other flaws can lead to remote code execution or lateral pivoting.

Immediate mitigation steps for site owners (practical, step-by-step)

Follow these steps immediately, in order:

1. Identify the plugin: In WordPress admin > Plugins, look for “WP Responsive Images”. Also check the filesystem: /wp-content/plugins/wp-responsive-images.
2. Deactivate the plugin: Use the admin UI to deactivate. If admin is unavailable, rename the plugin folder via SSH/FTP (for example, add .disabled) — WordPress will auto-deactivate it.
3. Block vulnerable endpoints: If you cannot remove the plugin immediately, block its delivery scripts at the webserver (.htaccess, nginx rules) or via perimeter controls. Deny any requests whose query string contains traversal tokens.
4. Temporary rule to block traversal in src:

   Block requests with src parameters that include ../ or encoded equivalents such as %2e%2e%2f. Example conceptual regex (test before applying):

   (?i)(src=.*(\.\./|%2e%2e%2f|%2e%2e\\))

   Implement carefully to avoid false positives. Limit the rule to the plugin path if possible.

5. Scan for signs of exploitation: Examine access logs for traversal attempts and requests referencing sensitive filenames. Check for unexpected downloads, new files, suspicious cron tasks, web shells, or ownership/permission changes.
6. Harden file access: Move wp-config.php above webroot if host permits. Ensure backups are not stored in public directories. Tighten file permissions so only required users can read secrets.
7. Rotate secrets: If you suspect exfiltration, change database passwords, API keys, and admin credentials immediately.
8. Monitor and retain logs: Keep webserver and application logs for at least 90 days where feasible. Alert on repeated traversal attempts against plugin endpoints.
9. Update or remove: When the plugin author releases a patch, update immediately. If the plugin is abandoned, remove it and replace with a maintained alternative or a safe custom implementation.

Secure coding guidance for plugin developers (how to fix it properly)

If your plugin serves files from disk based on user input, follow a deny-by-default model: canonicalize, validate, and restrict.

Key steps:

1. Canonical realpath checks: Compute the canonical real path of the requested file and ensure it resides within an allowed base directory.

<?php
$base_dir = realpath( WP_CONTENT_DIR . '/uploads/wp-responsive-images' ); // allowed directory
$requested = $_GET['src'] ?? '';

// Reject empty or suspicious input early
if ( empty( $requested ) ) {
    http_response_code(400);
    exit;
}

// Prevent null byte attacks
$requested = str_replace("\0", '', $requested);

// Normalize URL encoded characters
$requested = rawurldecode( $requested );

// Build full path and canonicalize
$fullpath = realpath( $base_dir . '/' . $requested );

if ( $fullpath === false || strpos( $fullpath, $base_dir ) !== 0 ) {
    // requested file is outside allowed directory
    http_response_code(403);
    exit;
}

// Serve file safely (consider permission checks)
?>

• Avoid using raw user-controlled filenames directly in file functions without sanitization.
• Normalize encodings and reject encoded traversal tokens early (e.g., %2e%2e%2f).
• Prefer internal identifiers or whitelists (IDs, DB mappings, manifests) rather than arbitrary file paths.
• Enforce MIME checks, set appropriate Content-Type, and avoid revealing filesystem paths in error messages.
• Log rejected traversal attempts with IP and user agent for later analysis.

WAF and perimeter rule examples (for administrators)

Below are conceptual patterns to help block exploitation attempts. Adapt to your infrastructure and test thoroughly to avoid false positives.

Block query strings containing traversal

• Plain traversal: ../
• Encoded: %2e%2e%2f, %2e%2e%5c, double-encoded variants like %252e%252e%252f

(\.\./|\.\.\\|%2e%2e%2f|%2e%2e%5c|%252e%252e%252f)

Example rule logic:

IF URI contains /wp-content/plugins/wp-responsive-images/ AND query string contains src= AND query string matches traversal regex → BLOCK.

Block requests for sensitive filenames

(wp-config\.php|\.env|id_rsa|database(\.sql|\.sql\.gz)|backup|dump)

Also consider rate limiting and temporary IP blocking for repeat offenders. Test in detection mode first, then move to blocking once confident.

Hardening server and WordPress configuration

• File permissions: set wp-config.php to 440 or 400 if feasible; avoid world-readable files.
• Remove backups from webroot; store backups in secure, access-controlled locations.
• Disable directory listing on Apache/Nginx.
• Ensure PHP errors are not displayed publicly; log to files instead.
• Keep WordPress, themes, and plugins updated; remove unused or abandoned plugins.
• Apply principle of least privilege for database and file accounts; use host-level isolation for multi-site environments.

If your website was compromised — recovery steps

1. Take the site offline or isolate the host to prevent further data leakage.
2. Preserve logs and create forensic copies before making changes.
3. Rotate credentials: database passwords, WordPress admin credentials, API keys, and any tokens found on the server.
4. Scan for backdoors and web shells using both signature and behavior-based methods. Look for recently modified files, obfuscated code (base64/eval), and unexpected cron jobs.
5. Replace compromised files with clean copies or restore from a trusted backup.
6. Rebuild access tokens and secure external services connected to the site.
7. Conduct a full security audit and, if required, engage professional incident response.

Detection: what to look for in logs and telemetry

• Access log entries with src= and traversal sequences (plain or percent-encoded).
• Successful 200 responses for requests targeting known sensitive filenames.
• New or unusual file downloads from plugin endpoints.
• Traffic spikes against plugin endpoints or repeated attempts from the same IP range.
• Malware scanner alerts referencing exfiltrated or suspicious file contents.

Responsible disclosure and developer guidance

Plugin developers should:

• Use canonicalization and strict directory checks (realpath-based) to prevent traversal.
• Sanitize and normalize input; reject encoded traversal tokens early.
• Add unit tests and fuzzing cases for path traversal patterns to prevent regressions.
• Provide a clear security contact and update timeline so users can respond promptly.
• When releasing fixes, provide clear upgrade instructions and mitigation guidance for users who cannot patch immediately.

Practical checklist — immediate actions for teams

For site owners/operators

• Check if WP Responsive Images is installed.
• Deactivate/remove the plugin if present.
• Implement perimeter rules to block traversal payloads targeting the plugin.
• Scan logs and notify stakeholders if suspicious activity is found.
• Remove backups and sensitive files from public web directories.
• Rotate credentials if there’s evidence of exfiltration.

For developers and maintainers

• Apply realpath-based canonicalization and deny-by-default file serving.
• Normalize input and reject encoded traversal tokens.
• Add unit tests for path traversal cases.
• Provide a fixed plugin release and clear upgrade guidance.

For security teams

• Deploy perimeter rules to block the vector and monitor for attempts.
• Monitor for exploitation attempts and anomalous file accesses.
• Prepare an incident response playbook for full compromise scenarios.

Final words — act quickly, be thorough

Path traversal vulnerabilities that lead to arbitrary file disclosure are highly damaging because they expose secrets that enable complete takeover. CVE-2026-1557 is unauthenticated and trivial to attempt — treat every vulnerable installation as urgent.

Practical immediate steps: remove or disable the plugin, deploy perimeter rules to block traversal, review logs, harden file access on the server, and rotate credentials if there is any sign of compromise. Maintain careful logging and alerting so attempts are visible early.

— Hong Kong Security Expert