Threat Intelligence Report — CVE-2026-87013

Executive Summary

CVE-2026-87013 is a denial-of-service vulnerability in Open WebUI, a self-hosted AI platform, affecting versions 0.10.0 through 0.11.0. An authenticated user can persist a cyclical parent relationship in the folder tree via POST /api/v1/folders/{id}/update/parent, then trigger resource exhaustion through folder tree traversal operations on DELETE /api/v1/folders/{id} and POST /api/v1/folders/{id}/read. The vulnerability carries a CVSS 3.1 base score of 4.3 (Low severity) and is fixed in version 0.11.1.

Technical Analysis

The vulnerability is classified as CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop'). The root cause is twofold, as described in the NVD advisory:

1. Missing hierarchy validation on parent reassignment: The endpoint POST /api/v1/folders/{id}/update/parent permitted an authenticated user to set a folder's parent to itself or to one of its own descendants. Under a correctly validated nested-set or adjacency-list model, this operation should be rejected because a folder cannot be its own ancestor. Because validation was absent, an attacker could persist a parent cycle into the stored folder hierarchy.

2. Unbounded tree traversal on read/delete: The folder tree walks executed by DELETE /api/v1/folders/{id} and POST /api/v1/folders/{id}/read did not maintain a set of visited folder identifiers. A traversal algorithm that follows parent/child pointers without a visited-set (or depth cap) will recurse or iterate indefinitely when it encounters a cycle. Each such request therefore consumes CPU and memory until the process is constrained, killed, or times out.

The critical property here is persistence. Unlike a transient request-flood DoS, the malformed state is stored in the application's data model. The condition "remain[s] stored until repaired," meaning every subsequent invocation of the affected traversal endpoints re-triggers the resource exhaustion—even after service restart—until the cycle is manually corrected. This shifts the flaw from a simple availability bug into a persistent stored DoS.

The attack surface is the REST API of a self-hosted deployment. Required privileges are low (PR:L) because any authenticated user with folder-management permissions can invoke the affected endpoints. No user interaction (UI:N) or confidentiality/integrity impact (C:N/I:N) is present; the sole impact is availability (A:L). The network attack vector (AV:N) and low attack complexity (AC:L) make exploitation straightforward once credentials are held.

No specific function names, traversal implementations, or database schema details are provided by the NVD description; the analysis above is confined to the endpoints and behaviors explicitly stated.

Exploitation Scenarios

No public proof-of-concept exists for CVE-2026-87013. The following attack chain is inferred strictly from the vulnerability class (CWE-835) and the endpoints named in the NVD description.

1. Reconnaissance / target identification: The attacker identifies an internet- or intranet-exposed Open WebUI instance running a vulnerable version (0.10.0 through 0.11.0). This can be achieved via Shodan queries for the Open WebUI login interface or by fingerprinting the /api/v1/folders API surface. The attacker must hold valid credentials (any authenticated account with folder access).

2. Triggering the flaw class (cycle creation): Authenticated, the attacker creates or selects two folders where one is a descendant of the other. The attacker then issues POST /api/v1/folders/{id}/update/parent, setting the parent of the ancestor folder to its own descendant (or to itself). Because the endpoint does not validate that the target parent is not the folder itself or a descendant, the request succeeds and the cycle is persisted in the folder hierarchy.

3. Payload/execution method: There is no code payload—the "payload" is the malformed parent relationship itself. To weaponize it, the attacker issues a request to DELETE /api/v1/folders/{id} or POST /api/v1/folders/{id}/read against any folder within the now-cyclic tree. The tree-walk logic, lacking visited-ID tracking, never terminates and consumes CPU and memory indefinitely.

4. Post-exploitation impact: The affected request(s) tie up server resources, degrading or denying service to legitimate users of the Open WebUI platform. Because the cycle is stored, the DoS condition recurs on every subsequent traversal request and survives service restarts; it persists "until repaired" (the cycle manually broken). The attacker can repeat the request to maintain continuous resource pressure. No data is exfiltrated, modified, or corrupted beyond the folder relationship itself.

Impact Assessment

• Availability (A:L): The primary and only CVSS-scored impact. Successful exploitation degrades or denies service by consuming CPU and memory on affected requests. The "Low" (rather than High) rating reflects that the exhaustion targets request-processing resources and can be interrupted by process termination, but the persistent nature of the stored cycle elevates operational risk in practice.
• Confidentiality (C:N) / Integrity (I:N): No impact scored. The flaw neither discloses nor alters protected data, aside from the deliberately malformed folder parent relationship.
• Scope (S:U): Impact is confined to the vulnerable Open WebUI component.
• Blast radius: All users of a given Open WebUI deployment are affected once the cyclic folder state exists, since the traversal endpoints are shared. Multi-tenant or shared-team instances face collateral DoS. Because exploitation requires authentication, the effective blast radius is limited to environments where untrusted or low-privileged users can create and manage folders—common in collaborative self-hosted deployments.

Business impact: For organizations relying on Open WebUI as an internal AI platform, a persisted DoS can disrupt AI-assisted workflows, degrade productivity, and require manual data repair. The self-hosted nature means remediation depends on the operator upgrading to 0.11.1.

Detection Guidance

Sigma Rule

title: Open WebUI Folder Parent Cycle DoS (CVE-2026-87013)
id: 6f1c9a2e-4b7d-4c1a-9d3e-87013a1b2c3d
status: experimental
description: Detects creation of a cyclic folder parent relationship followed by folder traversal requests targeting Open WebUI endpoints affected by CVE-2026-87013.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-87013
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
detection:
  selection_parent:
    cs-method: 'POST'
    cs-uri-stem|contains: '/api/v1/folders/'
    cs-uri-stem|endswith: '/update/parent'
  selection_traversal:
    cs-method:
      - 'POST'
      - 'DELETE'
    cs-uri-stem|contains: '/api/v1/folders/'
    cs-uri-stem|endswith:
      - '/read'
  condition: selection_parent or selection_traversal
fields:
  - c-ip
  - cs-uri-stem
  - cs-method
  - sc-status
falsepositives:
  - Legitimate folder reorganization and read operations
level: low

YARA Rule

rule CVE_2026_87013_OpenWebUI_Folder_Cycle_DoS
{
    meta:
        description = "Detects Open WebUI source/artifacts referencing the vulnerable folder parent update and traversal endpoints associated with CVE-2026-87013"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-87013"
        date = "2026-01-01"
        severity = "low"
    strings:
        $ep1 = "/api/v1/folders/" ascii wide
        $ep2 = "/update/parent" ascii wide
        $ep3 = "/read" ascii wide
        $ver1 = "0.10.0" ascii wide
        $ver2 = "0.11.0" ascii wide
    condition:
        uint16(0) == 0x5A4D or true
        and $ep1
        and ( $ep2 or $ep3 )
        and ( $ver1 or $ver2 )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-87013 Open WebUI Folder Parent Cycle DoS Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/api/v1/folders/"; http.uri; content:"/update/parent"; nocase; reference:cve,2026-87013; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-87013; classtype:attempted-dos; sid:202687013; rev:1;)

alert http any any -> any any (msg:"CVE-2026-87013 Open WebUI Folder Tree Traversal Trigger"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/api/v1/folders/"; http.uri; content:"/read"; nocase; reference:cve,2026-87013; classtype:attempted-dos; sid:202687014; rev:1;)

Elastic Detection

sequence by user.name with maxspan=10m
  [ network where http.request.method == "POST" and
      http.request.uri like "/api/v1/folders/*/update/parent" ]
  [ network where
      (http.request.method == "DELETE" and http.request.uri like "/api/v1/folders/*") or
      (http.request.method == "POST" and http.request.uri like "/api/v1/folders/*/read") ]

Splunk SPL Query

index=web
| eval uri = coalesce(uri, url, cs_uri_stem)
| where match(uri, "/api/v1/folders/.+/(update/parent|read)$") OR match(uri, "/api/v1/folders/[^/]+$")
| stats count by src_ip, uri, method, status
| where count > 5
| sort - count

Wazuh OSSEC Rule

<group name="openwebui,cve-2026-87013,">
  <rule id="202687013" level="6">
    <decoded_as>json</decoded_as>
    <field name="method">POST</field>
    <url>/api/v1/folders/</url>
    <description>CVE-2026-87013: Open WebUI folder parent update request (possible cycle creation).</description>
    <options>no_full_log</options>
  </rule>
  <rule id="202687014" level="6">
    <if_sid>202687013</if_sid>
    <url>/update/parent</url>
    <description>CVE-2026-87013: Open WebUI folder parent reassignment endpoint accessed.</description>
  </rule>
  <rule id="202687015" level="8">
    <decoded_as>json</decoded_as>
    <url>/api/v1/folders/</url>
    <regex type="pcre2">/api/v1/folders/[^/]+/read$</regex>
    <description>CVE-2026-87013: Open WebUI folder tree traversal triggered (potential persistent DoS).</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED per tracked sources. Although the NVD description states the issue is fixed in 0.11.1, no patch evidence is recorded from any tracked source (no vendor fix, workarounds, or affected-version metadata confirmed in the dataset). Treat as unpatched pending verification.

1) Immediate mitigations (until upgrade is verified):

• Restrict access to the Open WebUI API. Require authentication and limit folder-management privileges to trusted users only; the flaw requires authentication, so reducing account scope reduces exposure.
• Place the instance behind a reverse proxy/WAF and block or rate-limit requests to POST /api/v1/folders/{id}/update/parent, DELETE /api/v1/folders/{id}, and POST /api/v1/folders/{id}/read for untrusted clients.
• Monitor the folder hierarchy for self-referential/ancestor-descendant parent cycles and manually break any detected cycle (the DoS persists "until repaired").
• Apply process-level resource limits (CPU/memory cgroups) so a runaway traversal is contained and killed rather than exhausting the host.

2) Patch / upgrade steps:

• Upgrade Open WebUI to 0.11.1 or later (per the NVD description). Because patch confidence is 0/4, independently verify the release notes/fix before relying solely on the version bump.
• After upgrading, audit existing folder data for any persisted parent cycles introduced pre-patch and repair them.
• Restart the service post-upgrade and confirm the traversal endpoints enforce cycle/visited tracking.

3) Long-term hardening:

• Enforce validation that a folder's new parent is neither itself nor any descendant (reject cycles at the API layer).
• Implement visited-identifier tracking or depth limits in all tree-walk routines (delete, read, and any future traversal code).
• Add server-side validation of parent relationships at the data-access layer as defense in depth.
• Deploy the detection rules above to alert on parent-reassignment followed by rapid traversal requests.
• Track Open WebUI releases and subscribe to vendor advisories for follow-up patches.

References

• NVD — CVE-2026-87013: https://nvd.nist.gov/vuln/detail/CVE-2026-87013
• CWE-835 — Loop with Unreachable Exit Condition ('Infinite Loop'): https://cwe.mitre.org/data/definitions/835.html
• MITRE ATT&CK T1499 — Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/
• Open WebUI project (vendor): https://github.com/open-webui/open-webui
• FIRST EPSS: not yet scored for this CVE (no value available)

Exploit-in-the-wild / threat actor activity: No public PoC, exploit code, or Nuclei template is known, and CISA KEV does not list this CVE. There is currently no evidence of active exploitation campaigns.