CVE-2026-57576

Executive Summary

CVE-2026-57576 is a denial-of-service (DoS) vulnerability in the Plone content management system, specifically affecting the plone.app.dexterity content-type system and the plone.app.contenttypes package. An authenticated user with content-creation privileges can submit content objects with excessively long titles, descriptions, or uploaded-file names, driving Plone into an unresponsive state and rendering the resulting content difficult to edit or delete. With a CVSS base score of 6.5 (Medium), the flaw primarily threatens availability; the low-privilege authentication requirement (PR:L) lowers the bar for malicious or careless insiders, and the medium complexity-to-impact ratio makes it a realistic availability risk for internet-exposed or multi-tenant Plone deployments.

Technical Analysis

This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption). The core weakness lies in the absence of server-side length validation or truncation for user-supplied string fields on Dexterity-based content objects. When a user creates content, the title, description, and uploaded-file name fields are accepted and persisted without bounding their maximum length.

Attack surface: The affected surface is the authenticated content-creation workflow exposed through Plone's web interface and REST API. Any user with permission to add content (a common grant in collaborative CMS deployments) can reach the vulnerable input fields.

Mechanism: By supplying pathologically long values in one or more of these fields, the attacker forces backend processing and storage of oversized strings. Depending on the deployment, this can manifest as excessive memory allocation, database write amplification, template rendering latency, or index/render pipeline saturation. The described outcome — Plone becoming unresponsive and the resulting content becoming "difficult to edit or delete" — is consistent with resource exhaustion during request handling and/or downstream rendering of the stored oversized values. Because the content persists, the DoS effect can be recurring: each attempt to view, list, edit, or delete the malformed object may re-trigger the resource-heavy processing.

No specific code paths, function names, or parameter names are provided in the NVD description, so the exact validation entry point and the precise string-length threshold are unspecified. What can be asserted from the description is the vulnerability class (uncontrolled resource consumption via unbounded input length) and the affected components (the Dexterity content-type system and its bundled content types).

Affected versions:

• plone.app.dexterity: through 3.2.2; 4.0.0 through 4.1.2; 5.0.0
• plone.app.contenttypes: through 3.0.11; 4.0.0 through 4.0.9; 5.0.0

Patched versions:

• plone.app.dexterity: 3.2.3, 4.1.3, 5.0.1
• plone.app.contenttypes: 3.0.12, 4.0.10, 5.0.1

Exploitation Scenarios

Attack chain inferred from the vulnerability class (CWE-400) and the NVD description. No public PoC or exploit code is available; the sequence below is a class-level reconstruction, not a validated exploit.

1. Reconnaissance / target identification: The attacker identifies a Plone deployment (e.g., via the powered-by footer or CMS fingerprinting) and confirms they hold an authenticated account with permission to create content. In collaborative deployments, self-registration or provisioned contributor accounts satisfy this requirement.

2. Trigger of the flaw class: The authenticated user initiates content creation through the standard Plone content-editing interface or the REST API, populating the title, description, or uploaded-file name fields with an extremely long string. Because the application does not enforce a maximum length, the oversized value is accepted and stored.

3. Execution method (class-level): Submitting the malformed content causes the server to process and persist the oversized strings. Repeated submissions or interaction with the stored object — listing, rendering, editing, or deleting it — re-triggers expensive processing. The attacker has no need for any memory-corruption or injection primitive; the impact derives purely from uncontrolled resource consumption.

4. Post-exploitation impact: Plone becomes unresponsive to legitimate users, degrading or denying service. The persisted malformed objects remain in the content tree and can be difficult to edit or delete through the normal UI, complicating recovery. Persistent availability degradation is the primary outcome; there is no described confidentiality or integrity impact.

Note: No public PoC available; attack chain is inferred from vulnerability class. No specific endpoint paths, API parameters, or function names are provided by the source data and none are assumed here.

Impact Assessment

CVSS:3.1 base score 6.5 (Medium), vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H. Subscore analysis:

• Attack Vector (AV:N, Network): Exploitable remotely over the network; no local access required.
• Attack Complexity (AC:L, Low): No special conditions or race windows; the attacker needs only the ability to submit oversized input.
• Privileges Required (PR:L, Low): Requires an authenticated low-privileged account able to create content. This is the principal mitigating factor.
• User Interaction (UI:N, None): No victim interaction is required to trigger the condition.
• Scope (S:U, Unchanged): Impact is confined to the vulnerable component's security authority.
• Confidentiality (C:N, None): No data disclosure described.
• Integrity (I:N, None): No data tampering described.
• Availability (A:H, High): Confirmed high availability impact — unresponsive CMS and content that is difficult to edit or delete.

Business impact: For organizations running Plone as an intranet portal, public website, or knowledge base, the availability impact can halt content publishing, internal collaboration, and public-facing services. The persistence of malformed content extends recovery time and may require administrative or backend intervention. Blast radius scales with deployment exposure and the number of accounts holding content-creation privileges — larger, more permissive deployments have a wider set of potential exploit sources. The requirement for authentication bounds the risk from unauthenticated internet mass-scanning, but does not eliminate it: malicious insiders, compromised contributor accounts, and self-registered users on open deployments all qualify. There is no CISA KEV listing and no reported exploit-in-the-wild evidence, indicating the immediate threat level is driven by availability exposure rather than active exploitation.

Detection Guidance

Sigma Rule

title: Plone Excessive Length Content Creation (CVE-2026-57576)
id: 9f3c1a72-4b8e-4d1a-9c6f-2a7e5d0b8c31
status: experimental
description: Detects authenticated content creation in Plone with abnormally long title, description, or uploaded file name values consistent with CVE-2026-57576 DoS attempts.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-57576
author: valtersit.com
date: 2026-01-01
logsource:
  product: webserver
  service: http
detection:
  selection_method:
    cs-method:
      - 'POST'
      - 'PUT'
  selection_path:
    cs-uri-stem|contains:
      - '/++add++'
      - '/portal_factory'
      - '/@types'
  selection_length:
    - cs-uri-query|re: '.{2000,}'
    - sc-bytes|gte: 50000
  condition: selection_method and selection_path and selection_length
fields:
  - c-ip
  - cs-username
  - cs-uri-stem
  - sc-bytes
falsepositives:
  - Legitimate bulk content migration or import scripts
  - Large legitimate file uploads
level: medium
tags:
  - attack.t1499
  - cve.2026.57576

YARA Rule

rule CVE_2026_57576_Plone_Long_Content_Fields
{
    meta:
        description = "Detects oversized title/description/file-name values associated with CVE-2026-57576 Plone DoS"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-57576"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $field_title = "title"
        $field_desc1 = "description"
        $field_desc2 = "Description"
        $field_file = "filename"
        $json_type = "\"@type\""

    condition:
        filesize < 5MB and
        any of ($field_*) and
        (uint32be(0) == 0x7B0A2020 or $json_type) and
        filesize > 60000
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-57576 Plone Oversized Content Creation Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"++add++"; http.request_body; content:"title"; pcre:"/(title|description|filename)[^}]{2000,}/si"; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-dos; sid:202657576; rev:1; reference:cve,2026-57576; metadata:author valtersit.com;)

Elastic Detection

sequence by source.ip with maxspan=60s
  [http where http.request.method == "POST" and
    http.request.body.bytes > 50000 and
    (http.request.body.content : "title" or http.request.body.content : "description")]
  [http where http.request.method == "POST" and
    http.request.body.bytes > 50000]

Splunk SPL Query

index=web sourcetype=access_combined
| eval uri_len=len(uri), total_len=len(uri)+len(referer)
| where (cs_method="POST" OR cs_method="PUT")
    AND (like(uri, "%++add++%") OR like(uri, "%portal_factory%") OR like(uri, "%/@types%"))
    AND (bytes > 50000 OR uri_len > 2000)
| stats count, avg(bytes) as avg_bytes, max(bytes) as max_bytes by clientip, uri
| where count >= 5
| sort - count
| table clientip, uri, count, avg_bytes, max_bytes

Wazuh OSSEC Rule

<group name="plone,cve-2026-57576,">
  <rule id="100576" level="10">
    <if_sid>31100</if_sid>
    <id>^POST$|^PUT$</id>
    <match>++add++|portal_factory|/@types</match>
    <description>CVE-2026-57576: Possible Plone oversized content creation (DoS attempt)</description>
    <mitre>
      <id>T1499</id>
    </mitre>
    <group>dos,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The versions below reflect the fixed releases named in the NVD description; they are authoritative from the description but should be verified against the official Plone security advisory before deployment. No vendor workaround is provided in the source data.

1. Immediate mitigations:

• Restrict content-creation privileges to trusted, vetted accounts; audit and reduce the population of users with add-content permissions on exposed deployments.
• Place an upstream reverse proxy or WAF in front of Plone that enforces maximum request body size and rejects or truncates requests containing pathologically long string fields.
• Limit upload body sizes and set request timeouts to bound the resource cost of any single submission.
• Monitor for repeated oversized POST/PUT requests from the same account and rate-limit or temporarily suspend offending sessions.

2. Patch/upgrade steps:

• Upgrade plone.app.dexterity to 3.2.3, 4.1.3, or 5.0.1 (matching the deployed major line).
• Upgrade plone.app.contenttypes to 3.0.12, 4.0.10, or 5.0.1 (matching the deployed major line).
• Confirm the installed versions with the standard Plone add-on version listing, then restart the instance and validate that oversized input is now rejected.
• After patching, locate and remediate any pre-existing malformed content objects, which may still need backend intervention to edit or delete.

3. Long-term hardening:

• Adopt an application-layer input length policy for all user-supplied string fields, enforced server-side rather than only in the UI.
• Run periodic content audits to detect abnormal field lengths before they accumulate.
• Keep Plone core and all add-ons current by subscribing to official Plone security announcements.
• Apply defense-in-depth rate limiting and resource quotas so a single low-privileged account cannot exhaust server capacity.
• Integrate WAF logging and the detections above into the SOC monitoring pipeline to catch recurrence attempts.

References

• NVD — CVE-2026-57576: https://nvd.nist.gov/vuln/detail/CVE-2026-57576
• Plone Security Advisories (official vendor advisories for plone.app.dexterity / plone.app.contenttypes): https://plone.org/security
• CWE-400 — Uncontrolled Resource Consumption: https://cwe.mitre.org/data/definitions/400.html
• MITRE ATT&CK T1499 — Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/
• CISA Known Exploited Vulnerabilities Catalog (no entry for this CVE as of report date): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No threat actor campaigns or exploit-in-the-wild activity have been reported for CVE-2026-57576 at the time of writing. EPSS has not yet assigned a score, and no public PoC or Nuclei template is available.