CVE-2026-103388 in MISP
Summary
by MITRE • 09/30/2026
MISP renders the source field of a Galaxy Cluster as a clickable hyperlink whenever the stored value passes PHP's FILTER_VALIDATE_URL validation. Because FILTER_VALIDATE_URL accepts the javascript: URI scheme, a user with galaxy editor privileges on the local instance or on a synced instance could store a javascript: URL as the cluster source.
When another user views the affected Galaxy Cluster and clicks the rendered link, the embedded script executes in the victim's browser context, enabling session hijacking, data exfiltration, or actions performed on behalf of the victim.
Preconditions:
- Attacker must hold galaxy editor privileges (local or via sync).
- Victim must view the affected cluster and click the malicious link.
Impact:
- Stored cross-site scripting (XSS) in the victim's browser.
- Potential session theft, credential harvesting, or unauthorized actions within the MISP application.
Affected: <2.5.48.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified involves a stored Cross-Site Scripting flaw within the Misp Project software version 2.5.47 and earlier, specifically affecting how the system handles and renders the source field of Galaxy Clusters. The core technical issue stems from an insufficient validation mechanism in the PHP backend logic responsible for processing user input. When a value is stored as the cluster source, the application checks if it conforms to a valid URL format using the standard PHP FILTER_VALIDATE_URL function. While this filter generally ensures that the string resembles a web address, it does not restrict the URI scheme to safe protocols such as HTTP or HTTPS. Consequently, malicious actors can exploit this oversight by injecting javascript: URIs into the source field. Because the validation passes and the application subsequently renders this value as an interactive hyperlink without further sanitization of the protocol, any user viewing the cluster is presented with a clickable link that appears legitimate but contains executable client-side code.
This architectural flaw allows for persistent malicious content storage within the database, which aligns with CWE-79, known as Improper Neutralization of Input During Web Page Generation or Stored Cross-Site Scripting. The attack requires specific preconditions to be successful: an attacker must possess galaxy editor privileges on either a local instance or one that is synchronized with other instances in the network. This privilege level enables the insertion of the malicious javascript: URL into the cluster metadata. Once stored, the payload remains dormant until triggered by another user. When a victim navigates to view the affected Galaxy Cluster and interacts with the rendered source field by clicking the hyperlink, their browser interprets the URI scheme as an instruction to execute JavaScript code rather than navigate to a new page. This execution occurs within the security context of the MISP application domain, granting the attacker full access to the victim's session cookies, local storage data, and DOM elements.
The operational impact of this vulnerability is severe due to its potential for unauthorized actions performed on behalf of authenticated users. By executing arbitrary scripts in the victim's browser environment, an adversary can perform session hijacking by stealing authentication tokens or cookies, thereby gaining full control over the victim's account without needing their credentials. Furthermore, the attacker can harvest sensitive data displayed within the application interface, including threat intelligence indicators, organizational details, and private notes associated with Galaxy Clusters. The ability to execute actions on behalf of the user also means that an attacker could manipulate MISP configurations, create false reports, or exfiltrate large volumes of structured data by crafting automated requests using the victim's active session. This represents a significant breach of confidentiality and integrity within threat intelligence sharing platforms where trust between users is paramount.
From a defensive posture perspective, this vulnerability maps to MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter: JavaScript, as well as T1078, Valid Accounts, since the attack relies on legitimate user privileges to persist malicious content that exploits session validity. Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade the MISP instance to version 2.5.48 or later, where this validation logic has been corrected to explicitly whitelist allowed URI schemes such as http and https while rejecting dangerous protocols like javascript: data:, and vbscript:. For organizations unable to patch immediately due to operational constraints, implementing a Web Application Firewall rule that blocks requests containing javascript: URIs in the source field parameters can provide temporary protection. Additionally, enforcing strict Content Security Policy headers on the MISP deployment can mitigate the impact by preventing inline script execution or restricting the sources from which scripts are allowed to load, thereby neutralizing the payload even if it is successfully stored and rendered.