CVE-2026-3998 Overview
CVE-2026-3998 is a Stored Cross-Site Scripting (XSS) vulnerability in the WM JqMath plugin for WordPress, affecting all versions up to and including 1.3. The flaw resides in the style shortcode attribute of the [jqmath] shortcode. The generate_jqMathFormula() function concatenates the attribute directly into an HTML style attribute without calling esc_attr() or any equivalent output escaping. Authenticated users with Contributor-level access or above can inject arbitrary JavaScript that executes in the browsers of subsequent page visitors [CWE-79].
Critical Impact
Authenticated contributors can store malicious JavaScript that executes whenever any user, including administrators, views the affected page.
Affected Products
- WM JqMath plugin for WordPress, all versions through 1.3
- WordPress sites permitting Contributor-level account registration
- Any installation rendering the [jqmath] shortcode in published content
Discovery Timeline
- 2026-04-15 - CVE-2026-3998 published to the National Vulnerability Database
- 2026-04-22 - Last updated in NVD database
Technical Details for CVE-2026-3998
Vulnerability Analysis
The WM JqMath plugin renders mathematical formulas using the [jqmath] shortcode and accepts a style attribute to control inline CSS. The generate_jqMathFormula() function in wm_jqmath.php takes the user-supplied style value and concatenates it directly into the rendered HTML style attribute of the output element. WordPress shortcode attributes are user-controlled data, and any value reaching an HTML attribute context must be passed through esc_attr() to neutralize quotes and angle brackets.
Because neither sanitization on input nor escaping on output is applied, an attacker can break out of the style attribute and inject event handler attributes or close the tag entirely to insert <script> content. The injected payload is persisted in the post body and executed whenever a visitor renders the affected page, including authenticated administrators.
Root Cause
The root cause is missing output escaping in generate_jqMathFormula(). The function trusts the shortcode style attribute and writes it verbatim into an HTML attribute context. WordPress provides esc_attr() for exactly this case, but the plugin omits it. See the plugin source at wm_jqmath.php line 27 and line 33 for the vulnerable concatenation.
Attack Vector
An attacker authenticates with Contributor-level privileges or higher and creates or edits a post containing a [jqmath] shortcode. The attacker supplies a crafted style attribute that closes the original attribute and tag, then injects JavaScript through an event handler or <script> element. When an administrator previews or publishes the post, or any visitor views the page, the script executes in their browser context. This enables session theft, account takeover, or further administrative actions via forged requests. Refer to the Wordfence Vulnerability Report for additional technical detail.
Detection Methods for CVE-2026-3998
Indicators of Compromise
- Post or page content containing [jqmath] shortcodes with style attribute values that include quote characters, <, >, javascript:, or HTML event handlers such as onerror, onload, or onmouseover.
- Unexpected outbound requests from administrator browser sessions to attacker-controlled domains shortly after viewing posts authored by lower-privileged users.
- New administrator accounts or modified user roles created shortly after a Contributor edits a post containing the [jqmath] shortcode.
Detection Strategies
- Query the wp_posts table for post_content matching [jqmath combined with suspicious style values containing <, ", ', or on[a-z]+=.
- Inspect rendered HTML for style attributes containing script-like content or attribute-breakout sequences.
- Review WordPress audit logs for posts edited or created by Contributor accounts that include the [jqmath] shortcode.
Monitoring Recommendations
- Enable a web application firewall ruleset that inspects shortcode attribute payloads for XSS patterns.
- Monitor administrator session activity for unexpected privilege changes, plugin installs, or theme edits.
- Alert on new Contributor or Author accounts that immediately publish content using the [jqmath] shortcode.
How to Mitigate CVE-2026-3998
Immediate Actions Required
- Disable or remove the WM JqMath plugin until a patched release is installed.
- Audit existing posts and pages for the [jqmath] shortcode and remove or sanitize any suspicious style attribute values.
- Restrict Contributor and Author account creation, and review existing low-privilege accounts for unexpected activity.
- Force a password reset for administrator accounts that may have viewed attacker-controlled content.
Patch Information
No fixed version is referenced in the NVD entry at the time of publication. All versions up to and including 1.3 are vulnerable. Monitor the WordPress plugin repository and the Wordfence Vulnerability Report for an updated release that applies esc_attr() to the style shortcode attribute.
Workarounds
- Deactivate the WM JqMath plugin and replace it with an alternative math rendering plugin that escapes shortcode attributes.
- Apply a WAF rule blocking requests containing [jqmath combined with HTML breakout characters in the style parameter.
- Configure WordPress to require editor approval for all Contributor submissions before publication.
- Remove the unfiltered_html capability from any custom roles to limit injection surface area.
# Configuration example: disable the vulnerable plugin via WP-CLI
wp plugin deactivate wm-jqmath
wp plugin delete wm-jqmath
# Scan post content for suspicious shortcode usage
wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content REGEXP '\\[jqmath[^\\]]*style=[^\\]]*(<|on[a-z]+=|javascript:)'"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
