WordPress Contact Form Plugin Stores Malicious Scripts via IP Headers

The Contact Form by Supsystic plugin for WordPress is vulnerable to Stored Cross-Site Scripting via IP Address Header in all versions up to, and including, 1.10.2 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. An unauthenticated attacker can first call the 'updateNonce' action — which is accessible without authentication due to its absence from the plugin's permission list — to obtain a valid nonce, then submit a contact form with a malicious payload in a spoofed IP header such as X-Forwarded-For.

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 Contact Form by Supsystic plugin for WordPress contains a stored cross-site scripting (XSS) vulnerability that allows unauthenticated attackers to inject malicious scripts through IP address headers. This vulnerability affects all versions up to 1.10.2 and exploits insufficient input sanitization and output escaping. Because the vulnerability is stored rather than reflected, any user who visits a page containing the injected payload will execute the attacker's script, making this a particularly dangerous vector for compromising WordPress sites. Website owners using this popular contact form plugin are at immediate risk, especially since the attack requires no authentication and can be triggered through readily accessible plugin actions.

Casky's 323 mapped skills leverage Claude's extended reasoning to detect the attack patterns associated with TA0001 (Initial Access) and TA0043 (Reconnaissance) techniques underlying this CVE. Practitioners using Casky would identify detection signals including suspicious modifications to the Contact Form plugin's database entries, anomalous HTTP headers in request logs containing script tags or encoded payloads, and unexpected JavaScript execution contexts originating from form-related pages. The platform's skill set enables security teams to recognize the reconnaissance phase where attackers probe the 'updateNonce' action endpoint and the delivery phase where malicious IP headers are injected, allowing defenders to correlate these indicators and block exploitation before stored payloads reach end users.

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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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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-2026-83625.

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-2026-83625

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