WordPress Plugin Avatar Field Stored XSS Injection Flaw

The User Profile Builder – Beautiful User Registration Forms, User Profiles & User Role Editor plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Avatar Field in all versions up to, and including, 4.0.2 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 zero-length multipart file branch in wppb_save_avatar_value() writes the raw request value directly to user meta, bypassing the wppb_save_attachment_id()/wppb_verify_attachment_id() validation path; the stored payload is later adopted as a WordPress attachment URL and rendered unescaped by wppb_default_fields_make_upload_button() when an administrator views the affected account.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

The User Profile Builder plugin for WordPress contains a Stored Cross-Site Scripting (XSS) vulnerability in its avatar upload functionality that allows unauthenticated attackers to inject malicious scripts into user profiles. Due to insufficient input sanitization in the wppb_save_avatar_value function, attackers can craft specially-crafted multipart file submissions that bypass security controls. When legitimate users view an affected profile page, the injected scripts execute in their browsers with full session privileges, potentially leading to session hijacking, credential theft, or malware distribution. This vulnerability impacts all WordPress installations using the plugin up to version 4.0.2, affecting both site administrators and regular users who may unknowingly view poisoned profiles.

Casky's 323 mapped security skills leverage Claude AI's extended reasoning to detect the attack chains associated with MITRE techniques TA0001 (Initial Access) and TA0043 (Reconnaissance). The platform identifies the vulnerability through multiple detection vectors: recognizing insufficient output encoding patterns in avatar rendering code (CWE-79), detecting polyglot payloads in file upload handlers, and correlating suspicious script tags in user-generated content fields. Practitioners using Casky would observe findings highlighting the unescaped avatar field outputs, flagged multipart boundary manipulations, and JavaScript execution in profile contexts—providing actionable intelligence to patch systems before exploitation occurs and to audit existing user profiles for injected payloads.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-95866.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-95866

Casky has 323 skills that investigate the attack patterns behind CVE-2026-95866. Run one and get CVSS-scored findings in 3 minutes.

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