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Full vulnerability report · 2026
CVE-2026-16145High confidence

Invisible Anti-Spam & CAPTCHA <= 5.1 - Unauthenticated Stored Cross-Site Scripting via 'action' Parameter

matthiasnordwig · Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms

7.2HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Fix not verified
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-58864

No EUVD known-exploited evidence

The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'action' parameter in all versions up to, and including, 5.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The stored payload is written by any unauthenticated admin-ajax.php request whose action value matches an entry in the plugin's explicit-actions list, which is auto-populated for common form builders at activation and requires no authentication gate to reach the save path.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.2 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Fix not verified
01

What, why and how

The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'action' parameter in all versions up to, and including, 5.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The stored payload is written by any unauthenticated admin-ajax.php request whose action value matches an entry in the plugin's explicit-actions list, which is auto-populated for common form builders at activation and requires no authentication gate to reach the save path.

What

The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'action' parameter in all versions up to, and including, 5.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The stored payload is written by any unauthenticated admin-ajax.php request whose action value matches an entry in the plugin's explicit-actions list, which is auto-populated for common form builders at activation and requires no authentication gate to reach the save path.

Why

Attacker-controlled content can reach a browser as executable script without sufficient output encoding or sanitisation.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'action' parameter in all versions up to, and including, 5.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The stored payload is written by any unauthenticated admin-ajax.php request whose action value matches an entry in the plugin's explicit-actions list, which is auto-populated for common form builders at activation and requires no authentication gate to reach the save path.

Why

Attacker-controlled content can reach a browser as executable script without sufficient output encoding or sanitisation.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-79 ↗

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'). The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SChangedScope: The attack can affect a component governed by a different security authority.CLowConfidentiality impact: A successful attack can cause a limited loss.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-79
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-58864Official EUVD mapping

The Invisible Anti-Spam & CAPTCHA — reCAPTCHA Alternative for All Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'action' parameter in all versions up to, and including, 5.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The stored payload is written by any unauthenticated admin-ajax.php request whose action value matches an entry in the plugin's explicit-actions list, which is auto-populated for common form builders at activation and requires no authentication gate to reach the save path.

Official EUVD record
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Fix not verified
Affected
≤ 5.1
Fixed
No fixed version is explicitly recorded in the structured CVE data.
Action
No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 15 Aug 2026 · Last source change 18 Aug 2026, 19:38 UTC · CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-23
European sourceENISA EUVD · EUVD-2026-58864
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD not scheduled

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →
  1. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-58864↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-16145 · cve.blacktree.nl