Plugin Name	WP Responsive Images
Type of Vulnerability	Arbitrary File Download
CVE Number	CVE-2026-1557
Urgency	High
CVE Publish Date	2026-02-26
Source URL	CVE-2026-1557

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
Risk: Arbitrary file download (unauthenticated) via crafted src parameter

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 is a high‑risk, easily exploitable issue because it requires no authentication and can expose highly sensitive files (for example, wp-config.php, backups, private uploads, and other configuration files).

In this post we explain, in plain language and with pragmatic steps, what this vulnerability means for site owners and developers, how to detect signs of exploitation, immediate mitigations you can apply right now, secure code fixes developers should implement, and how managed firewall/virtual patching and site‑hardening can reduce your exposure while an official patch is released.

Note: This article is written by the WP‑Firewall security team. If you run WordPress sites, treat this as an urgent operational security advisory.

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Executive summary (what you need to know now)

• What it is: An unauthenticated path traversal vulnerability in the plugin’s code that processes an image src parameter. The vulnerability allows attackers to specify relative paths (like ../../) to retrieve files outside the plugin upload or images directory.
• What’s at stake: Attackers can download arbitrary files. These may include wp-config.php (database credentials), database backups, private uploads, .env files, SSH keys, or any file readable by the web server user.
• How easy is it to exploit: High. No authentication required and the vector is simple (malicious src values). This makes it attractive to automated scanning and mass exploitation.
• Immediate action: If you have the plugin installed, remove or disable it until a patched release is available. Implement WAF rules that block path traversal payloads and suspicious src parameters. Harden file permissions and move sensitive files out of the webroot if possible.
• Recovery if exploited: Treat it as a breach—audit logs, rotate all credentials (database, API keys, admin passwords), perform full malware and configuration inspection, and restore from a known clean backup if necessary.

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How the vulnerability works (technical but non-actionable)

At a high level, the plugin exposes functionality that accepts a src parameter and uses it to read and return files from disk. The vulnerability arises when this input is not normalized and validated. If the plugin simply concatenates the incoming src parameter with a base path (for example, /wp-content/plugins/wp-responsive-images/) and serves the content, an attacker can pass traversal sequences (../) or encoded variants (%2e%2e%2f) to jump outside the intended directory and access other files on the filesystem.

Why this is dangerous:

• The webserver process often has read access to files that contain secrets (wp-config.php, exported SQL files, plugin or theme configuration files).
• Attackers can script mass scans across many sites looking for this exact pattern.
• Once file content is obtained, attackers can escalate: they may extract DB credentials and then attempt to connect, or search for keys and tokens they can use against other services.

We will not publish a proof‑of‑concept payload because that would be irresponsible. Instead, the rest of this article focuses on detection, mitigation, and secure fixes.

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Affected components and typical request patterns

Affected: The plugin’s endpoint(s) that accept an image src (query string or form field) and serve files.

Typical suspicious request signs in access logs (examples for detection only):

• Requests that include src=../../ or src=%2e%2e%2f.
• Requests that attempt to fetch files named wp-config.php, database.sql, .env, id_rsa, or paths like /etc/passwd.
• Requests to plugin PHP endpoints with long traversal sequences or many encoded characters.

Look for:

• 200 responses to requests that ordinarily would not return content (e.g., a request that returns text/plain for a .php file).
• Unusual response sizes for plugin endpoints.
• Repeated requests from the same IPs for different sensitive filenames.

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Real‑world impact scenarios

1. Disclosure of database credentials (wp-config.php)
   • Consequence: Attacker can extract DB user/password and then attempt to connect to the database from the web host or elsewhere (if remotely accessible). From there they can read or modify data, exfiltrate user lists, etc.
2. Exposure of backup files stored in webroot
   • Consequence: Full site content and database exports can be stolen, giving attackers everything they need to clone the site or search for credentials.
3. Discovery of API keys or tokens
   • Consequence: Use of stolen tokens for external services, leading to additional compromise.
4. Combined attacks
   • Attackers may chain arbitrary file read with remote code execution in other vulnerabilities or use obtained credentials to pivot.

Because the exploit requires no authentication, the permitted risk is zero on public internet-exposed sites. Treat every vulnerable installation as high priority.

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

If you host WordPress sites, follow these steps immediately (in this order):

1. Identify whether the plugin is installed and active
   • WordPress admin > Plugins > look for “WP Responsive Images”.
   • Also scan your file system: /wp-content/plugins/wp-responsive-images.
2. If installed — deactivate the plugin
   • From the admin UI: click Deactivate.
   • If you cannot access the admin UI, rename the plugin folder via FTP/SSH (example: rename wp-responsive-images to wp-responsive-images.disabled). WordPress will automatically deactivate it.
3. If you’re not ready to remove it permanently, at minimum block the vulnerable endpoints
   • Block requests to the plugin’s delivery script(s) via webserver config, .htaccess, or your WAF.
   • Deny any requests whose query string contains traversal sequences (examples below).
4. Add a WAF rule (temporary virtual patch)
   • Block requests with src parameters that include ../ or URL‑encoded equivalents.
   • Block requests with src parameters that contain sequences like ..%2f and %2e%2e.
   • Example (conceptual regex to block malicious src values):

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

   Important: implement rules carefully to avoid false positives. If you use managed firewall tools, enable the rule as “block” for suspicious requests to the plugin path only.

5. Scan for signs of exploitation
   • Check access logs for requests that include src= with traversal sequences and for requests that reference known sensitive files.
   • Check for unexpected downloads of wp-config.php or other files.
   • Review the server for newly added files, suspicious cron tasks, web shells, unusual users, and sudden changes to ownership/permissions.
6. Harden file access
   • Move wp-config.php above the webroot if your host allows it.
   • Ensure web server user does not have unnecessary read permission on backup files or other sensitive artifacts.
   • Remove any database dumps or backups from public web directories.
7. Rotate secrets
   • If you suspect data was exfiltrated, rotate database passwords, API keys, and any credentials stored on the server that may have been compromised.
8. Monitor and log
   • Enable and retain logs (webserver, plugin, and WAF logs) for at least 90 days where feasible.
   • Set alerts for repeated 4xx/2xx responses hitting plugin endpoints.
9. Update or remove when patch is available
   • When the plugin author releases a patch, update immediately.
   • If the plugin is abandoned, remove it and replace functionality with a well‑maintained alternative or a custom safe implementation.

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

If you maintain WP Responsive Images or a similar plugin that serves files from disk based on user input, the secure pattern is clear: never trust user-supplied paths. Always canonicalize, validate, and restrict.

Key steps:

1. Use a canonical realpath check

   <?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)
   

2. Avoid direct inclusion of user-controlled filenames in file functions without sanitization.
3. Normalize encodings and reject encoded traversal sequences early (e.g., %2e%2e%2f).
4. Prefer using an internal identifier (ID) mapping to files (e.g., store accepted image names in DB or an allowed manifest) rather than passing arbitrary paths.
5. Enforce MIME checks, set appropriate Content-Type, and don’t reveal file paths in errors.
6. Log all attempts to access files via the plugin, including rejected traversal attempts, with IP and UA.

By design, file serving endpoints should perform strong deny-by-default checks and log suspicious activity for later analysis.

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WAF rule examples and patterns (for administrators)

Below are conceptual WAF rule patterns to help block exploitation attempts. These are illustrative; your WAF UI will differ and needs testing to avoid blocking legitimate traffic.

Block query strings containing traversal:

• Detect common traversal characters:
  • Plain: ../
  • Encoded: %2e%2e%2f, %2e%2e%5c, %2e%2e/, %252e%252e%252f (double-encoded)
• Example generic regex (for query string scanning):

(\.\./|\.\.\\|%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 seeking sensitive filenames:

• If request contains wp-config.php, /.env, id_rsa, database.sql, backup, etc., consider blocking or returning 404.

Example regex targeting filenames:

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

Rate limiting and IP reputation:

• Apply rate limits to endpoints under the plugin folder.
• Temporarily block IPs with repeated traversal attempts.

Note: Be careful with false positives. Test rules in detection/monitor mode first where possible, then switch to blocking when confident.

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Hardening server and WordPress configuration (recommended)

• File permissions: ensure wp-config.php is 440 or 400 where possible, not world-readable. The webserver user must read it but limit other account access.
• Remove backups from webroot: Store backups outside the public webroot or use secure storage with access control.
• Disable directory listing in Apache/Nginx.
• Ensure PHP errors are not displayed publicly; log instead.
• Keep WordPress, themes, and plugins updated. Remove unused or abandoned plugins.
• Use principle of least privilege for file and database accounts.
• Host-level isolation: if you run multiple sites, isolate them to prevent lateral movement.

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If your website was compromised — recovery steps

1. Take the site offline (maintenance mode) or isolate the host to prevent further data leakage.
2. Preserve logs (webserver, WAF, application) and create forensic copies.
3. Rotate credentials:
   • Database user password (update wp-config.php and apply new password).
   • All WordPress admin passwords and any API keys found on the server.
4. Scan for backdoors and web shells:
   • Use both signature and behavior-based scanners.
   • Look for recently modified files, unusual PHP code, base64 or eval chains, or cron jobs you did not create.
5. Replace compromised files with clean copies from a trusted source or restore from a clean backup.
6. Rebuild access tokens and ensure external services are secured.
7. Conduct a full security audit and consider professional incident response if you lack the experience.

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Detection: what to look for in logs and telemetry

• Access log lines with src= and .. sequences in the query string or percent-encoded forms.
• Successful (200) responses for requests that try to fetch known sensitive files.
• New or unusual file downloads from plugin endpoints.
• Suspicious spikes in traffic hitting plugin endpoints.
• Malware scanner alerts for suspicious content in downloaded files.

Set up detection rules to alert you immediately when the plugin endpoint is requested with traversal-like input.

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Responsible disclosure and developer guidance

If you are a plugin developer:

• Adopt secure input validation and canonicalization patterns like the realpath approach above.
• Sanitize, normalize, and strictly constrain file reads to known directories.
• Add unit tests and fuzzing cases for path traversal to prevent regressions.
• Provide a security contact or VDP for private reports and a clear update/patch timeline.
• When a vulnerability is reported, coordinate responsible disclosure: notify users, publish a fix, and provide guidance for mitigation until users can update.

As maintainers of plugins and themes, you are custodians of your users’ security. Path traversal and arbitrary file read are classic bugs that are easy to introduce but also easy to mitigate with the right checks.

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How a managed firewall (WAF) helps while you wait for an official patch

Managed WAFs offer several benefits in this exact scenario:

• Rapid virtual patching: a WAF rule can block exploit attempts at the perimeter before they reach your site.
• Signature updates: as researchers and vendors track new exploit patterns, WAFs can update rules centrally to protect millions of sites quickly.
• Layered defenses: WAFs combine rate limiting, IP reputation, and specific payload detections to reduce noise and stop brute force scans.
• Malware scanning: detect signs of exfiltration or web shells after the fact.
• Incident logging: consolidate logs of attempted exploitation for forensic analysis.

While a WAF does not replace a proper plugin security fix, it is one of the fastest effective defenses you can deploy to reduce risk immediately.

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WP‑Firewall recommendation: How we help and what you can do now

We take vulnerabilities like CVE‑2026‑1557 seriously. Our approach is practical:

• Immediate coverage: We provide managed WAF rules that block traversal attempts and suspicious src parameters before they reach your site.
• Malware scanning: Our scanner looks for signs of data leakage and web shells related to file read/exfiltration campaigns.
• Virtual patching: If a plugin you use is vulnerable and an official patch is not yet available, our virtual patching can block exploit attempts while you plan updates.
• Ongoing monitoring: We offer continuous logging and alerting so you can respond quickly to suspicious events.

If you host WordPress sites and want fast mitigation while you evaluate the plugin or wait for a patch, there are protective steps you can take immediately (see the “Immediate mitigation” section above). For many users, enabling a managed WAF and virtual patching is the fastest way to reduce exposure.

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Practical checklist — immediate actions for teams

For site owners/operators:

• ☐ Check if WP Responsive Images is installed.
• ☐ Deactivate/remove the plugin if present.
• ☐ Implement WAF 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 virtual patching rules to block the vector.
• ☐ Monitor for exploitation attempts and anomalous file accesses.
• ☐ Prepare incident response playbook for full compromise scenarios.

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Final words — act quickly, be thorough

Path traversal vulnerabilities that lead to arbitrary file disclosure remain one of the most damaging types of bugs, because they can expose the very secrets that let attackers take complete control. The fact that CVE‑2026‑1557 is unauthenticated and trivial to attempt makes it urgent for anyone running the affected plugin to act now.

Practical steps: remove or disable the plugin, deploy defensive WAF rules, review logs, and harden file access on the server. If you run many sites, adopt managed virtual patching to reduce the blast radius and give yourself time to properly update or replace the vulnerable plugin.

If you need help, WP‑Firewall provides fast, practical protections (including a free tier) you can enable immediately to reduce risk while you remediate. Start with the free plan to get essential defenses in place, and consider Standard or Pro plans if you require automated removal, virtual patching, and advanced support.

Stay safe, and please reach out to your security team if you find indicators of compromise — treat any suspected exploitation as a serious incident and act quickly.

— WP‑Firewall Security Team