CVE-2026-55248 in plone.app.portlets
Summary
by MITRE • 08/28/2026
plone.app.portlets provides portlets and a Plone-specific user interface for plone.portlets. Prior to 5.0.8, 6.0.4, and 7.0.2, a member who can add an RSS portlet can set its feed URL to a very large response, causing src/plone/app/portlets/portlets/rss.py to download and retain excessive data in memory and deny service. The same RSS URL handling accepts internal hosts, IP addresses, single-word domains, and explicit ports, allowing server-side requests that can probe internal network services and open ports. A malicious feed item can also supply a JavaScript URL that is retained as the item link and can execute script when used by a victim. The affected logic includes _rss_feed_url_validator, _normal_url_validator, RSSFeed._retrieveFeed, RSSFeed._buildItemDict, and the FEED_DATA in-memory cache. This issue is fixed in versions 5.0.8, 6.0.4, and 7.0.2.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability resides within plone.app.portlets, a widely used extension for the Plone content management system that provides portlet functionality and a specialized user interface. Prior to versions 5.0.8, 6.0.4, and 7.0.2, this component suffered from multiple critical security flaws related to input validation, resource management, and cross-site scripting. These issues stem primarily from insufficient sanitization of URLs provided by users when configuring RSS portlets, which allows attackers to exploit the server-side processing logic for denial of service, internal network reconnaissance, and client-side code execution.
The first major issue involves a lack of proper size constraints on feed data retrieval, leading to a Denial of Service condition classified under CWE-400: Uncontrolled Resource Consumption. When an authenticated user with permission to add RSS portlets configures the feed URL, the system invokes logic within src/plone/app/portlets/portlets/rss.py to fetch and parse the content. Specifically, functions such as _rss_feed_url_validator, RSSFeed._retrieveFeed, and RSSFeed._buildItemDict fail to enforce strict limits on the size of the response body. Consequently, an attacker can supply a feed URL that points to a resource returning excessively large responses. The application proceeds to download this data into memory without adequate checks, causing the server process to consume excessive RAM. This uncontrolled resource consumption eventually leads to service degradation or complete denial of service for other users and system resources.
Beyond resource exhaustion, the vulnerability includes severe Server-Side Request Forgery capabilities aligned with CWE-918: Server-Side Request Forgery (SSRF). The URL validation logic is permissive enough to accept internal hostnames, private IP addresses, single-word domains that resolve locally, and explicit port numbers. This allows an attacker to craft malicious feed URLs that force the Plone server to initiate HTTP requests to internal network services or open ports on local infrastructure. Such behavior enables attackers to probe the internal network topology, identify running services, and potentially interact with backend systems that are not exposed to the public internet. The FEED_DATA in-memory cache further exacerbates this by retaining references to these fetched resources, increasing the attack surface for subsequent exploitation attempts.
Additionally, the vulnerability encompasses a Stored Cross-Site Scripting flaw categorized under CWE-79: Improper Neutralization of Input During Web Page Generation. The RSS feed parsing logic retains JavaScript URLs within item links without proper sanitization or encoding. When an attacker submits a maliciously crafted RSS feed containing such entries, these scripts are stored in the database and subsequently rendered by victim browsers when they view the portlet content. This results in arbitrary script execution in the context of the vulnerable website, potentially leading to session hijacking, credential theft, or defacement. The combination of SSRF and XSS highlights a fundamental failure in input validation across both server-side processing and client-side rendering layers.
To mitigate these risks, organizations must immediately upgrade plone.app.portlets to version 5.0.8, 6.0.4, or 7.0.2, where the aforementioned logic has been corrected with stricter URL validation and resource limits. In environments where upgrading is not immediately feasible, administrators should implement network-level controls such as web application firewalls that block outbound requests from the Plone server to private IP ranges and restrict allowed ports for RSS feed retrieval. Furthermore, enforcing strict input sanitization on any custom portlet development or third-party integrations can help prevent similar vulnerabilities in related components. Regular security audits focusing on CWE-400, CWE-918, and CWE-79 patterns are recommended to ensure ongoing resilience against such attacks.