Nom du plugin	Redirection for Contact Form 7
Type of Vulnerability	Injection d'objets PHP
CVE Number	CVE-2025-8145
Urgence	Haut
CVE Publish Date	2025-08-19
Source URL	CVE-2025-8145

Critical: Unauthenticated PHP Object Injection in “Redirection for Contact Form 7” (<= 3.2.4) — What site owners must do now

Résumé

• A critical vulnerability (CVE-2025-8145) affecting the WordPress plugin “Redirection for Contact Form 7” (versions <= 3.2.4) allows unauthenticated attackers to perform PHP Object Injection (POI).
• CVSS: 8.8 (High). Attackers could chain POI into remote code execution, data exfiltration, or persistent backdoors if a gadget / POP chain exists in the site environment.
• Fixed in plugin version 3.2.5. Immediate remediation is required: update the plugin, or apply virtual patching and defensive controls if you cannot update immediately.
• This post is written from the perspective of WP‑Firewall’s security team and provides technical context, detection guidance, mitigations, and incident response recommendations for WordPress site owners and administrators.

Table of contents

1. Why this matters
2. What is PHP Object Injection (POI)?
3. How the Redirection for Contact Form 7 vulnerability is dangerous
4. Which sites are affected
5. Immediate steps (first 30–60 minutes)
6. Short-term mitigations (next hours)
7. Recommended WAF/virtual patch rules (examples and rationale)
8. Detection and hunting (logs, signatures, indicators)
9. Incident response and recovery (if you suspect compromise)
10. Hardening and long-term best practices
11. WP‑Firewall protection options (including our free plan)
12. Appendix: sample detection regex and monitoring queries

1 — Why this matters

If you run Contact Form 7 and you also use the “Redirection for Contact Form 7” plugin (wpcf7-redirect) on versions 3.2.4 or earlier, your site has a high‑risk vulnerability that can be triggered without authentication. PHP Object Injection can be a pivot-point for severe attacks: from remote code execution (RCE) and SQL injection to file system traversal and denial of service — depending on what code exists in your PHP ecosystem that can be abused (the so-called gadget or POP chain).

Because the vulnerability is unauthenticated and the plugin is commonly installed on sites that use Contact Form 7, this is an attractive target for automated exploits. You need to act now: either update to 3.2.5, or apply protective measures immediately.

2 — What is PHP Object Injection (POI)?

Short explanation

• PHP object injection occurs when unserialize() (or similar deserialization of PHP serialized strings) is called on attacker‑controlled data. If user input is passed into unserialize(), an attacker can craft a serialized object that, when reconstituted by PHP, invokes magic methods (e.g., __wakeup, __destruct) on classes present in the application or in installed libraries.
• If any of those classes perform dangerous actions (file write, eval, database queries, deletion), attackers can abuse the magic method behavior to perform actions with the privileges of the PHP process.

Why POI is high impact

• POI often leads to RCE if a gadget chain exists. Gadget chains can be composed from core WordPress code, plugin or theme classes, and third‑party libraries.
• Even where RCE is not possible, POI can enable persistent backdoors, modifications of site content, theft of sensitive configuration files (wp-config.php), or creation of new administrative users.

3 — How the Redirection for Contact Form 7 vulnerability is dangerous

What we know (safe, high‑level summary)

• The vulnerability allows attackers to send serialized PHP objects to a plugin-specific endpoint or functionality that is deserializing untrusted input.
• Because the flaw is exploitable by unauthenticated actors, an attacker only needs to craft an HTTP request to exploit the issue — there’s no prior access required.
• If a gadget chain exists on your site environment (and many WordPress installations include plugin or theme code or libraries that can act as gadgets), the impact can escalate from information disclosure to full site takeover.

Common exploitation paths

• Plugin receives POST or other input that is passed to unserialize() or a function that internally calls unserialize().
• Attacker posts a serialized object string that triggers a magic method on deserialized object(s).
• Magic methods perform filesystem or process-level actions (write to PHP files, modify options, run code), enabling persistent compromise.

4 — Which sites are affected

• Sites that have the plugin “Redirection for Contact Form 7” installed and active.
• Versions affected: <= 3.2.4 (the vendor has released a fixed version: 3.2.5).
• Even if you do not actively use the redirection features, simply having the plugin active and reachable on the site can be sufficient for exploitation.

5 — Immediate steps (first 30–60 minutes)

If you manage WordPress sites with the vulnerable plugin installed, do these immediate actions:

1. Update the plugin to 3.2.5 immediately
   – This is the single best action. Update from the WordPress admin (Plugins → Installed Plugins) or update via WP‑CLI: wp plugin update wpcf7-redirect
2. If you cannot update immediately, temporarily deactivate or remove the plugin
   – Deactivation: Plugins → Installed Plugins → Deactivate (fastest).
   – Removal is safer if you don’t need the functionality immediately. You can reinstall later from a patched source.
3. Enable firewall rules / virtual patching at the edge
   – If you run WP‑Firewall, enable our managed firewall + virtual patching. Our rules will block the most common exploitation patterns for this vulnerability even before the plugin is updated.
   – If you use other WAFs, add rules to block serialized PHP object payloads and requests targeting plugin-related endpoints.
4. Check logs (web server, WAF, application)
   – Look for suspicious POSTs to endpoints that the plugin exposes or to contact form endpoints with unusual payloads (serialized strings, especially starting with “O:” or “a:”).
   – If you see suspicious traffic, temporarily block the source IP and preserve logs for forensics.

6 — Short-term mitigations (next hours)

If you updated but want extra assurance, or if you had to postpone updating, these mitigations help reduce risk:

• Restrict access to endpoints that accept redirection parameters
  • If the plugin exposes endpoints under a predictable path, restrict access by IP or require known referrers where possible.
• Add WAF rules to block serialized PHP payloads
  • Many exploitation attempts will include serialized strings. Blocking requests that contain patterns like O:\d+:" ou a:\d+:{ can stop many malicious attempts (see examples in the appendix).
• Harden file permissions
  • Ensure the web server user cannot write arbitrary files into plugin or theme directories.
  • wp-config.php should be protected; move it up one directory where possible or set strict file permissions.
• Audit admin users and scheduled tasks
  • Check for new admin accounts, unexpected scheduled events (cron jobs), or new PHP files in wp-content/uploads or plugin directories.

7 — Recommended WAF/virtual patch rules (examples and rationale)

Below are example rule concepts you can deploy in a WAF or IDS. These are defensive examples intended for administrators; do not publish working exploit code.

Rule A — Block requests containing serialized PHP object patterns

• Rationale: Serialized PHP objects typically include “O:” (object) or “a:” (array) tokens with class names and property definitions.
• Example regex (conceptual):
  – PHP serialized object pattern: O:\d+:"[A-Za-z0-9_\\\x7f-\xff]+";\d+:{
  – PHP serialized array pattern: a:\d+:{
• Practical note: Apply this rule only on POST/PUT requests that target plugin endpoints or endpoints that are not expected to receive binary data or legitimate serialized content. Be cautious — some legitimate systems may send serialized content.

Rule B — Block requests with suspicious base64-encoded serialized strings

• Rationale: Attackers sometimes obfuscate payloads with base64. Detect base64 blocks followed by serialized patterns.
• Regex approach: detect common base64 range with serialized tokens when decoded.

Rule C — Protect plugin endpoint paths

• If the plugin registers REST or admin-ajax endpoints, create rules restricting the allowed methods, content types, and origins. Example:
  • Block non-POST or unexpected content-types to endpoints that should only receive form-encoded data.
  • Whitelist referrers if appropriate.

Rule D — Rate-limit and challenge suspicious traffic

• Rationale: Many exploit attempts are automated. Rate limiting or adding an interactive challenge (CAPTCHA, JS challenge) can stop mass exploitation.

Important operational advice

• Test rules on staging first to reduce the chance of false positives.
• Log and notify on blocked attempts — those logs will be invaluable for incident response.

8 — Detection and hunting (logs, signatures, indicators)

What to look for in logs

• HTTP requests containing “O:” or “a:” in POST payloads or as a parameter value.
• Unexpected large POST bodies to contact form endpoints or plugin-specific URIs.
• New admin users created in a short burst, or changes to options like siteurl/home.
• PHP files unexpectedly created or modified under wp-content/uploads, plugins, or themes.
• Outbound network traffic or scheduled tasks that you didn’t authorize.

Search queries (conceptual)

• Webserver (Apache/Nginx) access logs:
  grep -Ei 'O:[0-9]+:"|a:[0-9]+:{' /var/log/nginx/access.log
• WordPress logs / application logs:
  Search for POST requests to admin-ajax.php or other plugin endpoints containing serialized patterns.

Endpoint fingerprinting

If you can determine the plugin-specific endpoints or parameter names, add those to your monitoring and alerting rules.

9 — Incident response and recovery (if you suspect compromise)

If you find evidence of exploitation or signs of compromise, treat this as an incident and follow an IR plan:

1. Isolate the site
   Take affected site offline or put it behind an allowlist while you investigate to prevent further damage.
2. Preserve forensic data
   Make full backups of the webroot, database, and server logs before making changes.
   Collect webserver logs, PHP error logs, WAF logs, and any intrusion detection logs.
3. Scan and remove backdoors
   Use a trusted malware scanner to find suspicious files. Manual review is critical: look for obfuscated PHP files, code added to theme functions.php, or PHP files in uploads directories.
   Do not rely solely on plugin-scanners; attackers often hide code in places scanners miss.
4. Review accounts and credentials
   Reset admin user passwords and rotate any API keys or external credentials stored on the site.
   If wp-config.php has been exposed, rotate DB credentials and secrets (AUTH_KEY, SECURE_AUTH_KEY, etc.) and update the database / wp-config with new credentials.
5. Restore from clean backup if necessary
   If the site is deeply compromised, restore from a known-good backup taken before the compromise. Patch the vulnerability first (update plugin or remove) before bringing the restored site online.
6. Post‑incident hardening
   Apply the WAF/virtual patch rules described above.
   Review plugin inventory and remove unused plugins/themes.
   Conduct a security audit of all installed components.

10 — Hardening and long-term best practices

Reduce future exposure with the following:

• Keep everything updated
  Update WordPress core, plugins, and themes promptly. Vulnerabilities like this are common and repairs are often released quickly; staying patched is your best defense.
• Minimize installed plugins
  Each plugin increases attack surface. Remove unused plugins and prefer well-maintained plugins with strong update history.
• Least privilege
  Run with the principle of least privilege: limit plugin and file-write permissions for the web server user.
• Web application firewall / virtual patching
  Use a dedicated WAF that can deploy rule sets quickly for emerging vulnerabilities, to protect sites while updates are rolled out.
• Regular backups and test restores
  Backups are only useful if they’re restorable. Regularly test disaster recovery procedures.
• Monitor and alert
  Set up alerts for suspicious requests, file changes, or newly created admin users.

11 — WP‑Firewall protection options (our recommendation and free plan)

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As the WP‑Firewall security team, we designed a layered, practical approach so you can protect your site right away—even if you can’t immediately update every plugin. Our Free plan gives you essential protection that stops the most common exploitation techniques like the ones used for this POI vulnerability.

What you get with WP‑Firewall Basic (Free)

• Essential protection: fully managed firewall + WAF rules tuned for WordPress.
• Unlimited bandwidth (the firewall sits at the application edge).
• Malware scanner to detect suspect files and changes.
• Mitigation of OWASP Top 10 risks out of the box.

Why choose the Free plan first

• Fast: enable protection in minutes and block automated exploitation without changing your site code.
• Low risk: the Free plan includes the core WAF rules and scanning that will reduce your exposure while you schedule plugin updates and deeper investigations.

If you need more automated remediation and advanced controls, consider upgrading:

• Standard ($50/year) — adds automatic malware removal and the ability to blacklist/whitelist up to 20 IPs.
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Sign up now: https://my.wp-firewall.com/buy/wp-firewall-free-plan/
(Protect your site immediately, then update and harden from there.)

12 — Appendix: sample detection regex and monitoring queries

(Use in your WAF, SIEM, or log-parsing tools. Test in staging before enabling in production to avoid false positives.)

A. Simple serialized object detection (regex concept)

• PHP object serialized token:
  O:\d+:"[^"]+":\d+:{
• Example pattern to search in log data:
  grep -Eo 'O:[0-9]+:"[^"]+":[0-9]+:{' access.log

B. Serialized array detection:

• a:\d+:{
• Exemple:
  grep -Eo 'a:[0-9]+:{' access.log

C. Base64 encoded payload detection

• Base64 blocks followed by serialized token after decoding: look for long base64 strings in POST payloads.
• Example detection heuristic:
  Detect POST fields > 200 bytes composed of base64 alphabet (A-Za-z0-9+/=) and flag for review.

D. Admin-ajax / REST endpoint monitoring

• Monitor POSTs to admin-ajax.php or wp-json endpoints with unexpected payload sizes or content-types.
• Example query:
  Check webserver logs for POSTs to /wp-admin/admin-ajax.php or /wp-json/ containing ‘O:’ or unusually long values.

E. File system changes detection

• Monitor wp-content/uploads for newly created .php files. Alert on any PHP file creation in upload directories.
• Example inotify or filesystem watch rule:
  Watch /var/www/html/wp-content/uploads for writes of *.php and trigger alert.

Closing notes (straight talk)

This vulnerability is critical because it’s unauthenticated and exploitable via PHP deserialization—an attack vector that historically leads to some of the most severe website compromises. The single most important immediate action you can take is to update the Redirection for Contact Form 7 plugin to version 3.2.5 or later. If you are unable to update quickly, enable a capable WAF and apply virtual patching rules (as described here) to block attack attempts while you coordinate updates.

If you operate or maintain many WordPress sites, consider an approach that combines fast automated protection (managed firewall + virtual patches), continuous scanning, and an incident response playbook. WP‑Firewall’s free plan gives you an immediate protective layer while you coordinate updates and audits.

If you’d like assistance triaging logs, confirming compromise, or rolling out protective rules across multiple sites, our security team can help. Start with the free plan and upgrade if you need automated removal, virtual patching, or managed services.

Stay safe and treat this vulnerability like the urgent matter it is — update now, monitor your logs, and apply layered protection.

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Authors: WP‑Firewall Security Team
Date: 2025-08-19