CVE-2026-55248: plone.app.portlets vulnerable to denial of service via RSS feed portlet

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.4%, percentile 37: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 37% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes plone.app.portlets (PyPI) >= 7.0.0, <= 7.0.1, fixed in 7.0.2; plone.app.portlets (PyPI) >= 6.0.0, < 6.0.4, fixed in 6.0.4; plone.app.portlets (PyPI) < 5.0.8, fixed in 5.0.8. Check your lockfile, including transitive dependencies.

What it is

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 rssfeedurlvalidator, normalurlvalidator, RSSFeed.retrieveFeed, RSSFeed.buildItemDict, and the FEEDDATA in-memory cache. This issue is fixed in versions 5.0.8, 6.0.4, and 7.0.2.

From the GitHub advisory

Impact By adding an RSS portlet, and giving this a link to a very large file, a member can cause a denial of service attack, because Plone will use lots of memory. The member could also use different urls to try to get information about the internal network and open port numbers (SSRF). A malicious RSS feed could cause stored XSS, when the url of a feed item is a javascript url.

Patches The problem has been patched in plone.app.portlets.

For Plone 6.2: upgrade to plone.app.portlets 7.0.2 For Plone 6.1: upgrade to plone.app.portlets 6.0.4 For Plone 6.0: upgrade to plone.app.portlets 5.0.8

Workarounds If upgrading is not immediately possible:

- Restrict who can manage portlets: remove the plone.app.portlets.ManageOwnPortlets permission from untrusted roles, and limit Manage portlets to trusted administrators (usually this is already restricted to the Manager and Site Administrator roles). - Where the RSS portlet is not needed, unregister it so it cannot be added. This would need to be done by editing a portlets.xml in your own code, so it is not a quick fix.

Weakness type: CWE-400.

Product: plone.app.portlets (PyPI) · Assigned by: GitHub_M · Published: 2026-08-28

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.44% probability of exploitation activity in the next 30 days; percentile 37.

Timeline

• 2026-08-28 — CVE record last updated
• 2026-08-28 — CVE record published by GitHub_M
• 2026-08-28 — GitHub-reviewed advisory GHSA-x5g3-w747-2h8q published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-x5g3-w747-2h8q github.com
2. CVE.org record CVE-2026-55248 cve.org
3. NVD entry CVE-2026-55248 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com
5. github.com github.com

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