CVE-2026-11511: Bolt CMS XSS Vulnerability

CVE-2026-11511 Overview

CVE-2026-11511 is an HTML injection vulnerability affecting Bolt CMS versions up to 3.7.5. The flaw resides in src/Storage/Field/Type/TextType.php within the HTML Attribute Handler component. Attackers can manipulate the style argument to inject arbitrary HTML content into rendered pages. The vulnerability is remotely exploitable and requires low privileges with user interaction. A public exploit exists, increasing exposure for affected deployments. The Bolt CMS GitHub repository has been archived and set to read-only, meaning the project is no longer supported by its maintainer. Organizations running unsupported Bolt CMS installations remain exposed without a vendor-supplied fix. This issue is categorized under [CWE-74] for improper neutralization of special elements in output.

Critical Impact
A public proof-of-concept exists for an unpatched HTML injection flaw in an abandoned CMS, enabling remote content manipulation against any site still running Bolt CMS 3.7.5 or earlier.

Affected Products

Bolt CMS versions up to and including 3.7.5
src/Storage/Field/Type/TextType.php component
HTML Attribute Handler functionality processing the style argument

Discovery Timeline

2026-06-08 - CVE-2026-11511 published to NVD
2026-06-08 - Last updated in NVD database

Technical Details for CVE-2026-11511

Vulnerability Analysis

The vulnerability resides in the TextType field handler responsible for rendering text-based content fields in Bolt CMS. The handler accepts a style argument intended to control presentation attributes on rendered HTML elements. Improper neutralization of this input allows an attacker to break out of the attribute context and inject additional HTML markup. Because the injection occurs through an authenticated content management interface, low-privileged users with content editing rights can poison stored content. Site visitors subsequently rendering the affected pages receive attacker-controlled HTML. The attack vector is network-based with low complexity, though it requires user interaction to trigger the rendered payload.

Root Cause

The root cause is missing or insufficient sanitization in TextType.php when the HTML Attribute Handler processes the style argument. Special characters that should be encoded or stripped are passed through to the rendered output. This permits markup injection rather than confining input to a safe attribute value. The issue maps to [CWE-74], improper neutralization of special elements in output used by a downstream component.

Attack Vector

An authenticated attacker with content editing permissions submits crafted input through fields handled by the vulnerable TextType processor. The style argument is supplied with characters designed to terminate the attribute and introduce new HTML structures. When the affected content is rendered to other users, the injected markup executes within the page context. The vulnerability does not require elevated privileges, and publicly available exploit material lowers the barrier to abuse. Refer to the VulDB advisory for CVE-2026-11511 for additional technical details.

Detection Methods for CVE-2026-11511

Indicators of Compromise

Unexpected HTML tags or attributes appearing in stored content fields rendered through TextType
Web server logs showing POST requests to Bolt CMS content editing endpoints containing encoded angle brackets or quote characters within style parameters
Outbound requests from visitor browsers to unexpected domains after viewing Bolt CMS pages
Modifications to content records by low-privilege editor accounts followed by anomalous page renderings

Detection Strategies

Inspect Bolt CMS database content fields for HTML markup outside expected formatting, particularly within fields processed by TextType.php
Implement web application firewall rules to flag requests containing suspicious payloads targeting style parameters in Bolt CMS admin endpoints
Correlate editor account activity with rendered page changes to identify unauthorized content manipulation

Monitoring Recommendations

Enable verbose access logging on Bolt CMS administrative routes and forward logs to a centralized analytics platform
Monitor for new or unusual outbound connections from clients viewing CMS-rendered pages
Track editor and contributor account activity for unexpected content modifications across CMS records

How to Mitigate CVE-2026-11511

Immediate Actions Required

Migrate away from Bolt CMS 3.x to a supported content management platform, since the upstream project is archived and will not receive fixes
Restrict content editing privileges to a minimal set of trusted users until migration is complete
Deploy a web application firewall with rules to block HTML injection patterns targeting Bolt CMS admin endpoints
Review all existing stored content for injected markup and sanitize records as needed

Patch Information

No official patch is available. The Bolt CMS GitHub repository has been archived by its owner and is read-only. The maintainer no longer supports the affected versions. Organizations must rely on compensating controls or migrate to an actively maintained CMS to remediate the issue.

Workarounds

Apply a downstream sanitization layer such as HTML Purifier to content rendered by Bolt CMS before serving it to end users
Configure a strict Content Security Policy to limit the impact of injected markup in rendered pages
Disable or restrict access to content fields processed by the vulnerable TextType handler where business requirements allow
Audit user roles and remove content editing permissions from accounts that do not require them

bash

# Example Content-Security-Policy header to limit injected markup impact
add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self'; object-src 'none'; base-uri 'self'; frame-ancestors 'none'";