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CVE-2026-65556 – Unauthenticated PHP Object Injection – WPBruiser {no-Captcha anti-Spam} WordPress P

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Summary

CVE-2026-65556 is an unauthenticated PHP Object Injection vulnerability in the WPBruiser {no-Captcha anti-Spam} WordPress plugin (package goodbye-captcha) by MihChe, affecting all versions up to and including 3.1.43. The flaw stems from deserialization of untrusted data (CWE-502) and carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: Deserialization of untrusted data (CWE-502), allowing PHP Object Injection.
  • Trigger conditions: Exploitable by an unauthenticated attacker with no user interaction and low attack complexity.
  • Attack vector: Network — remotely exploitable over HTTP/HTTPS.
  • Impact: High impact to confidentiality, integrity, and availability, enabling full compromise of the affected system.

Affected software

  • WPBruiser {no-Captcha anti-Spam} (goodbye-captcha) by MihChe — versions up to and including 3.1.43.

Severity

  • CVSS v3.1 base score: 9.8 (Critical)
  • Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Update WPBruiser {no-Captcha anti-Spam} to a version later than 3.1.43 once released by the vendor.
  • If no patch is available: Restrict or deactivate the plugin until a fixed release is deployed, and place the site behind a WAF to filter untrusted serialized payloads and requests targeting the plugin’s endpoints.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw HTTP response body: /wp-content/plugins/goodbye-captcha/

References

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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

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  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
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