CVE-2026-92567

Executive Summary

CVE-2026-92567 is an authorization bypass vulnerability (CWE-639 — Authorization Bypass Through User-Controlled Key) in the TDuck survey form product affecting versions through 5.0. The flaw resides in the POST /user/form/data/update endpoint, which fails to validate that the authenticated user submitting an update actually owns the target form submission, allowing any authenticated user to overwrite other users' form response data. Because form responses frequently contain personal data, successful exploitation enables unauthorized modification (integrity impact: High) of arbitrary victim submissions, though confidentiality and availability are not directly affected.

Technical Analysis

The vulnerability class here is CWE-639: Authorization Bypass Through User-Controlled Key, also known as an Insecure Direct Object Reference (IDOR) tied to an ownership/authorization check. The core mechanism is a classic missing-object-level-authorization defect: the server-side handler for POST /user/form/data/update accepts a submission identifier from the request and performs the data write operation without verifying that the authenticated principal owns the referenced submission record.

Key technical points derivable from the supplied data:

• Endpoint: POST /user/form/data/update — a state-changing (write) endpoint used to update form submission data.
• Authentication requirement: The attacker must be authenticated (PR:L, network-accessible AV:N). This is not an unauthenticated flaw; a valid low-privilege account is sufficient.
• Root cause: Absence of an ownership validation check on the object key supplied by the client. The application trusts the client-provided submission identifier (the user-controlled key) and authorizes the write based solely on the fact that a session is authenticated, rather than checking that submission.owner == current_user.
• Identifiers: The description states that submission identifiers are "allocated in narrow ranges," meaning identifiers are short, sequential, or otherwise predictable (e.g., small integers). This makes object enumeration trivial and dramatically lowers the effort required to locate victim records.
• Complexity: AC:L — no special conditions, race windows, or elevated privileges are required. The attack is straightforward replay/modification of a single request.
• Scope: S:U — impact is confined to the vulnerable component.

No function names, code paths, or parameter names beyond the documented endpoint are provided, and none are invented here. The precise request body schema is not specified in the available data; the attack surface is defined by the documented endpoint and the identity of the submission being targeted.

Exploitation Scenarios

No public proof-of-concept, Nuclei template, or exploit code is available (PoC Status: None). The following chain is inferred strictly from the vulnerability class and the NVD description; it does not rely on fabricated implementation details.

1. Reconnaissance / target identification. The attacker obtains a legitimate, authenticated account on the TDuck instance (self-registration or a low-privilege account). The attacker locates the survey/form application, confirms the endpoint POST /user/form/data/update is reachable, and observes that submission identifiers returned to the user (for their own submissions) follow a narrow, predictable range.

2. Triggering the flaw class. Because identifiers are allocated in narrow ranges, the attacker enumerates candidate submission identifiers by incrementing/fuzzing near their own known identifier. Each candidate is submitted to POST /user/form/data/update using the attacker's valid session. The endpoint performs no ownership validation, so requests targeting submissions owned by other users are accepted rather than rejected with an authorization error.

3. Payload / execution method (class level). The attacker reissues the update request with a target submission identifier they do not own and supplies modified form-response values in the request body. There is no need to forge tokens, intercept traffic, or possess victim credentials — the sole bypass is the absent ownership check. At the class level this is a direct object-reference manipulation: substituting the victim's identifier into an otherwise-valid authenticated write request.

4. Post-exploitation impact. The attacker achieves unauthorized modification of arbitrary victims' form submissions. Given that form responses commonly contain personal data, this results in data tampering, corruption of survey integrity, potential injection of falsified responses, and possible second-order effects where downstream processes trust the overwritten data. Confidentiality and availability are not directly impacted; the sole high-rated impact is integrity (I:H).

Caveat: No specific parameter names, request schemas, or code-level function calls are asserted here because they are not present in the supplied data.

Impact Assessment

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

• AV:N (Network) — the endpoint is reachable over the network; no local access required.
• AC:L (Low) — no specialized conditions; the attacker simply needs to supply a different identifier.
• PR:L (Low) — a single authenticated low-privilege account is sufficient.
• UI:N (None) — no victim interaction is required; the attacker acts unilaterally.
• S:U (Unchanged) — impact remains within the vulnerable component.
• C:N (None) — the flaw does not directly expose confidential data to the attacker.
• I:H (High) — arbitrary modification of other users' submission data constitutes a serious integrity compromise.
• A:N (None) — no direct availability impact.

Business impact: Organizations using TDuck through version 5.0 to collect surveys, feedback, or forms containing personal data face a data-integrity risk: legitimate responses can be silently altered, falsified, or destroyed by any authenticated user. This undermines the trustworthiness of collected data, may violate data-integrity obligations under privacy regimes, and could poison downstream analytics, reporting, or decisions based on form data.

Blast radius: Any multi-user TDuck deployment (Internet- or intranet-facing) where submissions from different users are stored in a shared, sequentially-numbered space is affected. Because identifiers are narrow-range, the effective blast radius is all submissions, not merely those adjacent to the attacker's own.

Unaffected dimensions: No confidentiality leak and no direct denial-of-service are indicated by the CVSS vector. EPSS has not been scored by FIRST.org at the time of writing — no EPSS value is asserted.

Detection Guidance

Sigma Rule

title: TDuck Authorization Bypass - Cross-User Form Data Update (CVE-2026-92567)
id: 8b0f3e2c-1a4d-4c9e-9f21-tduck92567
status: experimental
description: Detects POST requests to the TDuck /user/form/data/update endpoint that update form submissions, indicative of CWE-639 cross-user object tampering.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-92567
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
  product: generic
detection:
  selection_endpoint:
    cs-method: 'POST'
    cs-uri-stem|endswith: '/user/form/data/update'
  condition: selection_endpoint
fields:
  - c-ip
  - cs-method
  - cs-uri-stem
  - cs-uri-query
  - sc-status
falsepositives:
  - Legitimate users updating their own submissions
level: medium
tags:
  - attack.t1190
  - cve.2026-92567

YARA Rule

rule CVE_2026_92567_TDuck_AuthBypass_Endpoint
{
    meta:
        description = "Detects references to the vulnerable TDuck update endpoint associated with CVE-2026-92567"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-92567"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $ep1 = "/user/form/data/update" ascii wide nocase
        $prod = "TDuck" ascii wide nocase

    condition:
        $ep1
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-92567 TDuck Authorization Bypass - /user/form/data/update POST"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/user/form/data/update"; nocase; classtype:attempted-user; reference:cve,2026-92567; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-92567; sid:202692567; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=5m
  [ network where http.request.method == "POST" and
      endsWith(http.request.path, "/user/form/data/update") ]

Note: EQL rules observe request flows. Pair this with an application-layer authorization check at the edge/proxy to flag cross-user object identifiers once the submission schema is known.

Splunk SPL Query

index=web sourcetype=access_combined
| search method="POST" uri_path="/user/form/data/update"
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, uri_path, status
| where count > 5
| sort - count

Wazuh OSSEC Rule

<group name="web,td諭uck,cve-2026-92567,">
  <rule id="10092567" level="10">
    <decoded_as>web-accesslog</decoded_as>
    <match>POST</match>
    <regex>/user/form/data/update</regex>
    <description>CVE-2026-92567: TDuck form data update request - possible authorization bypass (CWE-639)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_92567,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source.

1. Immediate mitigations

   • Restrict network access to the TDuck application to trusted users/networks where feasible; reduce the pool of authenticated accounts that can reach POST /user/form/data/update.
   • Place a reverse proxy or WAF in front of the application and enforce per-object authorization at the edge where the submission schema is known; alert on and rate-limit bulk/sequential identifier updates from a single principal.
   • Audit and monitor for anomalous update activity (one user updating many distinct submission identifiers) using the detection content in this report.
   • Back up form submission data to allow restoration of tampered responses and to reconstruct integrity.

2. Patch / upgrade steps

   • No vendor fix, workaround, or patch is currently documented (Patch Confidence 0/4). Contact the TDuck maintainers for a fix timeline.
   • Monitor the TDuck project and the NVD record (CVE-2026-92567) for advisory or release updates.
   • If a fixed version is published, upgrade all instances and verify the POST /user/form/data/update handler enforces an explicit owner == authenticated_user check before any write.

3. Long-term hardening

   • Enforce server-side object-level authorization on every state-changing endpoint; never authorize writes based solely on session validity.
   • Replace narrow-range, sequential submission identifiers with unguessable values (e.g., UUIDs) to make enumeration infeasible.
   • Apply consistent access-control review (e.g., OWASP Top 10 A01:2021 Broken Access Control) across the application.
   • Log and alert on authorization-relevant events, retaining records of which principal modified which submission.

References

1. NVD — CVE-2026-92567: https://nvd.nist.gov/vuln/detail/CVE-2026-92567
2. CWE-639 — Authorization Bypass Through User-Controlled Key: https://cwe.mitre.org/data/definitions/639.html
3. MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
4. OWASP Top 10 A01:2021 — Broken Access Control: https://owasp.org/Top10/A01_2021-Broken_Access_Control/
5. CVE Program — CVE-2026-92567 record: https://www.cve.org/CVERecord?id=CVE-2026-92567

Exploit-in-the-wild / campaign note: No CISA KEV listing, no public PoC, no Nuclei template, and no exploit code were identified for CVE-2026-92567 at the time of writing. There is no evidence of active exploitation or known threat actor campaigns.