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Technical Analysis of CVE-2026-54720
Silverstripe Framework is a PHP framework that powers the Silverstripe CMS. In versions prior to 6.2.2, the “Insert media from web” functionality in the CMS is vulnerable to a Cross-Site Scripting (XSS) attack originating from a specially crafted embed. This vulnerability was discovered by Jack Wallace from Bastion Security and assigned the identifier CVE-2026-54720.
The root cause of this vulnerability lies in the insufficient sanitization of user-supplied data within the oEmbed integration. When a user utilizes the “Insert media from web” feature, the CMS fetches metadata from a provided URL via the oEmbed protocol. The vulnerability manifests when an attacker supplies a malicious URL that returns a crafted oEmbed JSON response.
The oEmbed response contains an HTML attribute which is used to replace the embed shortcode within the CMS content. Due to improper neutralization of input during web page generation, this attribute is not adequately sanitized. Consequently, an attacker can inject arbitrary HTML and script code into the oEmbed response. When this malicious embed is rendered in the CMS, the injected script executes in the context of the victim’s browser.
The attack vector is network-based, requiring low attack complexity and no privileges. However, user interaction is required, as the victim must be tricked into following a specially crafted link or interacting with the malicious embed. Successful exploitation could allow a remote attacker to steal sensitive information, alter the appearance of the web page, or perform phishing and drive-by-download attacks.
The vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’). It affects all Silverstripe Framework versions prior to 6.2.2. The issue was addressed and fixed in version 6.2.2.
DailyCVE Form:
Platform: Silverstripe Framework
Version: < 6.2.2
Vulnerability: Cross-Site Scripting (XSS)
Severity: MEDIUM (CVSS 5.4)
date: 2026-07-01
Prediction: Patch available (2026-06-24)
What Undercode Say:
Analytics
- Attack Vector: NETWORK
- Attack Complexity: LOW
- Privileges Required: NONE
- User Interaction: REQUIRED
- Scope: UNCHANGED
- Confidentiality Impact: LOW
- Integrity Impact: LOW
- Availability Impact: NONE
- CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Exploit: (Educational Purposes!)
To reproduce this vulnerability, an attacker can host a malicious oEmbed endpoint that returns a crafted JSON response. For example:
Malicious oEmbed endpoint response
{
"type": "rich",
"html": "<img src=x onerror=alert('XSS')>",
"width": 200,
"height": 100
}
When a CMS user inserts media from the attacker-controlled URL, the `html` field is rendered unsanitized, executing the JavaScript payload.
Protection
- Upgrade Silverstripe Framework to version 6.2.2 or later.
- Apply the security patch provided by the vendor.
- Sanitize all oEmbed responses, especially the `html` attribute, before rendering.
- Restrict the use of the “Insert media from web” feature to trusted users only.
Impact
- Confidentiality: Low impact; potential for information theft.
- Integrity: Low impact; possible defacement or content manipulation.
- Availability: No impact.
- Successful exploitation can lead to session hijacking, credential theft, and phishing attacks.
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Sources:
Reported By: github.com
Extra Source Hub:
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