CVE-2026-103999: Ultra Addons for Contact Form 7 <= 3.5.54 - Unauthenticated Stored Cross-Site Scripting via File Upload

Q: Which deployments are exposed?

All versions of the Ultra Addons for Contact Form 7 WordPress plugin through 3.5.54 are affected. The issue is exploitable without authentication.

Q: What does an attacker need to upload to exploit this?

An attacker can bypass the extension blocklist with a text-type file such as .txt, .csv, .vtt, .srt, or .asc. The file can be classified as text/plain even when its contents begin with an HTML payload such as a BODY tag with an onload handler.

Q: What is the impact after a malicious file is uploaded?

The uploaded payload can create stored cross-site scripting in affected pages. Arbitrary web scripts execute when a user accesses an injected page, with potential confidentiality and integrity impact.

Q: How can defenders look for potential exploitation?

Review uploaded text-type files associated with the plugin, particularly .txt, .csv, .vtt, .srt, and .asc files whose initial contents contain HTML or script-bearing event handlers. Also review affected pages for unexpected injected content that could execute in visitors' browsers.

Published Oct 16, 2026

Updated

The Ultra Addons for Contact Form 7 plugin for WordPress is vulnerable to Stored Cross-Site Scripting via File Upload in all versions up to, and including, 3.5.54 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 extension blocklist gatekeeper is bypassed by uploading text-type files (.txt, .csv, .vtt, .srt, .asc) whose contents begin with an HTML payload such as '<BODY onload=…>', as the check classifies these files as text/plain without inspecting their byte content.

Affected Software

1 affected component

Ultra Addons Ultra Addons for Contact Form 7<=3.5.54

Event History

Oct 16, 2026

CVE Published

via MITRE·05:30 AM

Data Sourced

via MITRE·05:30 AM

DescriptionSeverityWeakness

Frequently Asked Questions

Which deployments are exposed?

All versions of the Ultra Addons for Contact Form 7 WordPress plugin through 3.5.54 are affected. The issue is exploitable without authentication.

What does an attacker need to upload to exploit this?

An attacker can bypass the extension blocklist with a text-type file such as .txt, .csv, .vtt, .srt, or .asc. The file can be classified as text/plain even when its contents begin with an HTML payload such as a BODY tag with an onload handler.

What is the impact after a malicious file is uploaded?

The uploaded payload can create stored cross-site scripting in affected pages. Arbitrary web scripts execute when a user accesses an injected page, with potential confidentiality and integrity impact.

How can defenders look for potential exploitation?

Review uploaded text-type files associated with the plugin, particularly .txt, .csv, .vtt, .srt, and .asc files whose initial contents contain HTML or script-bearing event handlers. Also review affected pages for unexpected injected content that could execute in visitors' browsers.

CVE-2026-103999: Ultra Addons for Contact Form 7 <= 3.5.54 - Unauthenticated Stored Cross-Site Scripting via File Upload

Affected Software

Event History

Frequently Asked Questions

Which deployments are exposed?

What does an attacker need to upload to exploit this?

What is the impact after a malicious file is uploaded?

How can defenders look for potential exploitation?

Company

Resources

Contact

Frequently Asked Questions

Which deployments are exposed?

What does an attacker need to upload to exploit this?

What is the impact after a malicious file is uploaded?

How can defenders look for potential exploitation?