TL;DR

• Vulnerability: Unauthenticated information disclosure in WebP Express (≤ 0.25.9), CVE-2025-11379.
• Risk level: Low-to-moderate (CVSS 5.3) for direct exploitation, but leaked information can enable follow-on attacks.
• Immediate actions:
  • Remove or deactivate the plugin if you do not need it.
  • If you must keep it, restrict access to plugin endpoints via webserver rules or an application firewall and rotate any secrets that may have been exposed.
  • Monitor logs for suspicious requests to plugin paths and unusual outbound connections from the server.

Background: What was disclosed

On 3 December 2025 a researcher reported an unauthenticated information exposure issue in the WebP Express plugin for WordPress (affecting versions up to and including 0.25.9). The issue has been assigned CVE-2025-11379.

In plain terms: an unauthenticated visitor (not logged in) can access data produced or stored by the plugin that should only be available to administrators or the server. The leaked data can include internal file paths, conversion/cache metadata, configuration values and, depending on deployment, environment details. While this vulnerability does not by itself allow arbitrary code execution, the reconnaissance value of the exposed information can materially increase risk from subsequent attacks (targeted uploads, credential theft, host pivoting, etc.).

The issue aligns with OWASP A3: Sensitive Data Exposure. Severity assessments place it in the low-to-medium range for direct impact, but the downstream risks from leaked information can be significant.

Why this matters: the real risk from “just data”

Information disclosure often gets short shrift compared with remote code execution, but it is a common enabler for more damaging attacks:

• Reconnaissance multiplier: Enumerated server paths, config values or plugin internals let attackers craft precise follow-on attacks—finding writable directories, backup files, or endpoints to abuse.
• Credential compromise: Revealed API keys, tokens or DB hints can lead to lateral access.
• Targeting and social engineering: Knowledge of technologies and versions improves phishing and targeted attack success.
• Increased scanning and follow-up: Once a host shows indicators, it can be queued for more aggressive scanning and exploitation.

In sum: information leakage often converts into higher-impact compromise when combined with other weak points.

How the vulnerability typically looks (high-level)

To defend effectively, administrators should understand the likely mechanics without sharing exploit details:

• A publicly reachable plugin endpoint returns or exposes internal data when invoked by an unauthenticated HTTP request.
• The endpoint might be a REST route, a direct script under the plugin directory, or an AJAX action lacking proper authentication checks.
• Returned data can include:
  • File paths or directory listings for cache and conversion folders.
  • Conversion logs or status dumps that expose server-side error messages.
  • Configuration values containing hostnames, URLs or API endpoints.
• Root cause is typically missing or incorrect permission checks or oversharing of debug information.

Automated scanners will flag this as medium risk; attackers use such details as breadcrumbs for targeted exploitation.

What administrators should not do

• Do not test exploitation on third-party sites — it is illegal and unethical.
• Do not publish exploit code or detailed request payloads that trigger the leak.
• Do not ignore the issue because it is labelled “low” — information disclosure can compound with other vulnerabilities.

Detection: what to look for in logs and monitoring

Audit server and application logs for suspicious activity. Prioritise high-value and publicly accessible sites.

• HTTP requests to plugin-specific paths such as:
  • /wp-content/plugins/webp-express/
  • Any publicly reachable script or REST route within that plugin folder
• Unusual GET/POST requests that return HTTP 200 with detailed JSON, XML or HTML containing file paths or server messages.
• Repeated requests from the same IP (or small set of IPs) across multiple hosted sites, especially to plugin endpoints.
• Requests with scanning-like query strings, suspicious headers or automated user-agents.
• Spikes in failed login attempts after suspected reconnaissance; attackers often follow reconnaissance with credential attacks.

Practical log search ideas (tool-specific syntax will vary):

• Search for requests containing “webp-express” in the request path.
• Filter responses by content type and size (e.g., JSON responses larger than expected).
• Correlate suspicious requests with CPU/IO spikes or outbound connection anomalies.

Immediate mitigation steps (quick, practical)

Prioritise mitigation on high-traffic and high-value properties first.

1. Inventory and prioritise:
   • Identify all sites running WebP Express and record their plugin versions.
   • Notify site owners and stakeholders for managed environments.
2. Recommended immediate actions:
   • Deactivate the plugin if it is not required for site operation.
   • Apply webserver-level restrictions to block direct access to the plugin directory or specific endpoints suspected of leakage.
   • Examples:
     • Apache/.htaccess: deny access to the plugin folder for unauthenticated or external requests.
     • Nginx: return 403 for requests matching /wp-content/plugins/webp-express/* unless authenticated.
   • If you rely on WebP Express for image conversion, consider temporary alternatives such as server-side conversion tools until a patched release is available.
3. Rotate and audit secrets:
   • If any API keys, tokens or credentials may have been exposed, rotate them promptly.
   • Audit access logs for unusual activity tied to those keys.
4. Harden file and directory permissions:
   • Ensure the webserver user cannot serve or execute files in unintended directories.
   • Restrict public access to plugin caches, logs and tmp folders.
5. Increase monitoring and alerting:
   • Add log alerts for requests to plugin paths and the indicators described in the Detection section.
   • Monitor for new domains/IPs requesting multiple distinct paths across several sites.
6. Consider removal:
   • If the plugin is not essential and no secure replacement exists, uninstall it until a patch is available.

Web application firewall (WAF) as an immediate safeguard

Deploying a WAF or applying equivalent webserver rules is one of the fastest ways to reduce exposure.

How a WAF helps:

• Blocks unauthenticated requests targeting known vulnerable endpoints.
• Provides virtual patching—preventing access to the vulnerable functionality while the plugin remains installed.
• Rate-limits or blocks scanning behaviour to slow mass exploitation attempts.

Recommended WAF controls for this issue:

• Block or challenge requests to plugin paths (for example, any request containing /wp-content/plugins/webp-express/ from unauthenticated IPs).
• Deny requests with signs of automated scanning (suspicious user-agents, rapid request bursts).
• Inspect response content and block requests that trigger disclosure patterns (responses containing ‘/wp-content/uploads’ or other internal path strings).
• Apply virtual patch signatures that target known request patterns used to trigger the leak.

If you do not currently run a WAF, implement webserver-level rules as described in the Immediate mitigation steps while you arrange for more comprehensive protections.

Longer-term fixes and hardening

• Patch management:
  • Track security advisories for WebP Express and apply vendor fixes when available.
  • Implement a plugin update policy: test updates in staging, schedule updates, and maintain compatibility checks.
• Least privilege:
  • Minimise the number of plugins performing sensitive tasks.
  • Ensure sensitive operations require appropriate capability checks in code.
• Disable verbose diagnostics in production:
  • Ensure plugins do not output detailed server-side error messages to unauthenticated requests.
• Secure development practices:
  • Adopt automated security scans, threat modelling and code review focused on access control.
• Network segmentation:
  • Limit access to administrative APIs and internal endpoints to specific IP ranges or authenticated channels.
• Backups and recovery:
  • Maintain off-site or air-gapped backups and regularly test restore procedures.

Incident response playbook (concise)

If you detect abuse or signs of compromise related to this vulnerability, follow these steps:

1. Contain
   • Remove or deactivate the vulnerable plugin.
   • Apply webserver-level restrictions and WAF rules.
   • Block offending IPs and ranges temporarily.
2. Investigate
   • Review access logs for suspicious requests predating the mitigation.
   • Check for unexpected file changes, backdoors or new admin users.
   • Inspect outbound connections and database access logs.
3. Eradicate
   • Remove injected files and restore from a known-clean backup if necessary.
   • Rotate credentials, API keys and tokens that might have been exposed.
   • Harden file permissions and configurations.
4. Recover
   • Reinstall clean copies of WordPress and plugins from trusted sources.
   • Re-apply security controls and test in staging before going live.
5. Post-incident
   • Document timeline, root cause and lessons learned.
   • Review monitoring, processes and controls to reduce recurrence risk.

Example WAF rule ideas (conceptual)

Below are high-level defensive patterns you can implement in a WAF or via webserver rules. These are for mitigation only and do not provide exploit instructions.

• Block unauthenticated access to plugin directories: If the request URI contains /wp-content/plugins/webp-express/ and the request is not from an authenticated admin session, return 403.
• Rate-limit and challenge scanning behaviour: If an IP makes > X requests to distinct plugin paths in Y seconds, challenge with CAPTCHA or temporarily block.
• Block suspicious response patterns: If a response contains internal path sequences (e.g., /var/www/, wp-content/uploads), block the request and log details for investigation.
• Monitor and alert: Generate alerts for 200 OK responses from plugin endpoints that include file-path strings or debug output.

Frequently asked questions (FAQ)

Q: If the plugin is exposing configuration, do I need to rotate my database password?

A: Rotate any credentials or keys that are plausibly exposed. If you see evidence a specific secret was leaked (for example, an API endpoint or token present in plugin output), rotate it immediately and audit access logs.

Q: Can a WAF fully protect me if I keep the plugin active?

A: A WAF can block exploitation vectors, provide virtual patching and reduce scanning noise. However, the only complete fix is to apply a vendor patch or remove the vulnerable plugin. Use WAF protections as a temporary mitigation while you patch.

Q: Is this vulnerability being actively exploited in the wild?

A: After disclosure, automated scanners and opportunistic exploitation attempts are common. Assume scanning is occurring and act quickly.

Q: My hosting provider manages my site — do I still need to act?

A: Yes. Confirm with your host whether they have applied protections or blocked vulnerable paths. Hosts may provide edge protection, but you should verify and monitor for access to relevant endpoints.

Final recommendations and next steps

1. Check immediately which of your sites run WebP Express (versions ≤ 0.25.9).
2. Decide between temporary deactivation or applying webserver/WAF-based blocking for plugin endpoints.
3. Use a WAF or webserver rules to virtual patch the vulnerability while you plan for a permanent fix.
4. Rotate any credentials that might have been exposed and audit logs for suspicious activity.
5. Implement longer-term controls: routine plugin updates, least-privilege practices and staging testing of updates.

As security professionals in Hong Kong advising regional and international operators, our guidance is: act swiftly, prioritise critical assets, and limit exposed attack surface until a vendor patch is applied. If you require third-party incident support, engage a reputable incident response provider and ensure they operate under clear terms and legal authority.

— Hong Kong Security Expert