CVE-2026-89406

Executive Summary

CVE-2026-89406 is a Missing Authorization (CWE-862) vulnerability in the Modula Image Gallery – Photo Grid & Video Gallery WordPress plugin, affecting all versions up to and including 3.0.1. The flaw allows unauthenticated attackers to disclose the contents of private galleries — including image titles, descriptions, dimensions, and original upload URLs — by abusing an improperly guarded metadata callback registered on the wp_head hook. Successful exploitation enables direct, unauthenticated retrieval of original private image bytes and provides a reliable mechanism for enumerating private modula-gallery posts. The vulnerability is rated CVSS 7.5 (High) with a C:H confidentiality impact; no patch is currently available.

Technical Analysis

The root cause is an authorization failure in the Modula_Meta::add_metas() method. This function is registered to the WordPress wp_head action, meaning it executes on every frontend request site-wide, not only on gallery-specific views. Within that hook, the plugin resolves an attacker-supplied post identifier using get_post( $_GET['modula_gallery_id'] ).

Three distinct defensive failures compound to produce the vulnerability:

1. Broken input guard. The gallery-side input validation intended to restrict execution is logically defective: it invokes empty('modula_gallery_id') against a nonempty string literal rather than against the $_GET parameter itself. Because a nonempty string literal is never empty, the guard evaluates to false unconditionally and never blocks the code path.

2. Insufficient object validation. The only check performed on the resolved object is that its post type equals modula-gallery (post_type === 'modula-gallery'). No validation of the target post's post_status occurs, so private (and other non-public) gallery posts are accepted and processed.

3. Missing capability check. No is_user_logged_in() call and no current_user_can('read_post', $gallery_id) capability verification are performed. The code therefore treats an unauthenticated request as authorized to read metadata for any modula-gallery post.

When these conditions coincide, the plugin emits Open Graph / Twitter Card meta tags into the response <head> for the targeted gallery — including the gallery member attachments' title, description, dimensions, and the original upload URL. The original upload URL is the critical disclosure: it points directly at the privately stored original image file, which can then be fetched without authentication. The result is both a confidentiality breach (metadata and full-resolution private media) and an enumeration primitive, since the modula_gallery_id parameter can be iterated to identify valid private gallery posts.

The attack surface is the public frontend HTTP interface of any WordPress installation running the affected plugin; no account, session, or privilege is required (AV:N, AC:L, PR:N, UI:N).

Exploitation Scenarios

No public proof-of-concept is available for CVE-2026-89406; the attack chain below is inferred from the vulnerability class and the behavior described in the NVD entry. It uses only parameters and identifiers explicitly referenced in that description.

1. Reconnaissance / target identification. An attacker identifies WordPress sites running the Modula Image Gallery plugin at version 3.0.1 or earlier. This is typically achieved through passive fingerprinting of plugin assets or through internet-wide scanning services that index the plugin's frontend paths. The presence of the plugin is the primary target qualifier; the vulnerabilities are unconditional on any page load once the plugin is active.

2. Triggering the flawed code path. The attacker issues an unauthenticated HTTP GET request to any frontend URL on the target site. Because Modula_Meta::add_metas() is hooked to wp_head, the callback runs on every frontend request. The attacker supplies the modula_gallery_id GET parameter with a candidate post identifier. The intended input guard fails (it tests a string literal rather than the parameter), so execution proceeds regardless of the parameter's value.

3. Payload / execution method. This is a parameter-tampering attack at the HTTP request layer; no code injection is involved. The attacker iterates candidate values of modula_gallery_id. For each value, the plugin calls get_post() on the supplied identifier. The sole object validation is the post_type === 'modula-gallery' check; posts of other types are ignored, but any modula-gallery post — including those with a private post_status — passes. Because there is no is_user_logged_in() or current_user_can('read_post', $gallery_id) enforcement, the request is treated as authorized.

4. Post-exploitation impact. For each valid gallery identifier, the response's <head> contains Open Graph / Twitter meta tags disclosing the gallery's member attachment metadata: image title, description, dimensions, and the original upload URL. The attacker harvests these values across enumerated identifiers to build a map of private galleries and their media. The disclosed original upload URLs are then requested directly, allowing unauthenticated download of the original private image bytes. The combined result is full confidentiality loss for private gallery content and a durable enumeration capability that persists until the plugin is patched or neutralized.

Notably, no interaction with the WordPress administrative interface, no authentication, and no user action are required (UI:N), making the exploitation loop trivially automatable.

Impact Assessment

The CVSS v3.1 base score is 7.5 (High) with the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. The subscores translate to concrete risk as follows:

• Confidentiality: High (C:H). Private gallery metadata and original full-resolution image files are disclosed. Original uploads may contain more data than rendered derivatives (higher resolution, embedded EXIF, and in some cases content the publisher intended to keep private).
• Integrity: None (I:N). The vulnerability does not permit modification of data.
• Availability: None (A:N). No denial-of-service condition is described.
• Attack Vector: Network (AV:N) / Complexity: Low (AC:L) / Privileges: None (PR:N) / User Interaction: None (UI:N). Any internet-reachable instance is exploitable by an unauthenticated remote actor with standard HTTP tooling.

Blast radius. Every WordPress site running Modula Image Gallery 3.0.1 or earlier is in scope. Because the callback executes on all frontend requests, exposure is not limited to pages that intentionally embed a gallery. Impacted assets include private or unlisted galleries used for client proofs, embargoed product photography, member-only media, and any imagery whose original URL was assumed to be non-discoverable. For organizations using galleries to gate content, the disclosure subverts the access control model entirely.

Secondary risk arises from enumerated original upload URLs: those URLs may be indexed, cached, or mirrored by third parties, meaning the disclosure can outlive a subsequent patch. The absence of public exploit code and CISA KEV listing indicates no confirmed in-the-wild exploitation at the time of writing, but the low complexity and unauthenticated nature of the flaw make weaponization straightforward — defenders should treat the exploitation window as open for the entire unpatched period.

Detection Guidance

Sigma Rule

title: Modula Image Gallery Private Content Disclosure via modula_gallery_id Parameter
id: 8f3b2c14-5a7d-4e91-b0c6-2d9e6f1a7c33
status: experimental
description: Detects unauthenticated requests abusing the Modula_Meta::add_metas() wp_head callback to enumerate private modula-gallery posts via the modula_gallery_id GET parameter.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-89406
author: valtersit.com
date: 2026/01/01
logsource:
  category: webserver
  product: apache
detection:
  selection_param:
    cs-uri-query|contains: 'modula_gallery_id='
  selection_method:
    cs-method: 'GET'
  condition: selection_param and selection_method
fields:
  - c-ip
  - cs-uri
  - cs-uri-query
  - cs-user-agent
falsepositives:
  - Legitimate gallery pages that pass a modula_gallery_id parameter during normal rendering
level: medium
tags:
  - attack.t1213
  - cve.2026-89406

YARA Rule

rule CVE_2026_89406_Modula_Missing_Authorization
{
    meta:
        description = "Detects Modula Image Gallery plugin versions vulnerable to unauthenticated private gallery disclosure (CVE-2026-89406)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-89406"
        date = "2026-01-01"

    strings:
        $func   = "Modula_Meta" ascii
        $metas  = "add_metas" ascii
        $hook   = "wp_head" ascii
        $param  = "modula_gallery_id" ascii
        $ptype  = "modula-gallery" ascii
        $guard  = "empty(" ascii

    condition:
        uint32(0) == 0x3C3F7068 and
        all of ($func, $metas, $param, $ptype) and
        any of ($hook, $guard)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-89406 Modula Image Gallery Private Content Disclosure Attempt"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"modula_gallery_id="; http.uri; content:"modula_gallery_id="; fast_pattern; classtype:attempted-recon; reference:cve,2026-89406; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-89406; metadata:created_at 2026_01_01, updated_at 2026_01_01; sid:202689406; rev:1;)

Elastic Detection

sequence by source.ip with maxspan=30s
  [ network where http.request.method == "GET" and
      url.query contains "modula_gallery_id=" ]
  [ network where http.request.method == "GET" and
      url.query contains "modula_gallery_id=" ]

Splunk SPL Query

index=web sourcetype=access_combined
| eval decoded_uri = urldecode(uri_query)
| where match(decoded_uri, "modula_gallery_id=") AND method="GET"
| stats count AS attempts, dc(clientip) AS unique_sources,
        values(uri_path) AS paths, earliest(_time) AS first_seen,
        latest(_time) AS last_seen
        by clientip, decoded_uri
| where attempts > 5
| sort - attempts

Wazuh OSSEC Rule

<group name="web,wordpress,modula,">
  <rule id="2026894" level="8">
    <if_sid>31100</if_sid>
    <url>modula_gallery_id=</url>
    <description>CVE-2026-89406: Modula Image Gallery private content disclosure attempt via modula_gallery_id parameter</description>
    <mitre>
      <id>T1213</id>
    </mitre>
    <group>cve_2026_89406,</group>
  </rule>

  <rule id="2026895" level="11" frequency="10" timeframe="60">
    <if_matched_sid>2026894</if_matched_sid>
    <same_source_ip />
    <description>CVE-2026-89406: Possible automated Modula gallery enumeration from single source</description>
    <group>cve_2026_89406,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations. Because no vendor fix exists, containment must be applied at the perimeter or platform layer.

   • Disable or deactivate the Modula Image Gallery plugin on any site where private or unlisted galleries are in use until a fixed release is available. If galleries must remain live, restrict them to fully public content only.
   • Block unauthenticated requests that supply the modula_gallery_id GET parameter at the WAF or reverse-proxy layer, and alert on repeated values from a single source (enumeration pattern).
   • Where gallery media is served from a protected store, move original uploads behind access controls that do not rely on URL obscurity.
   • Rate-limit and monitor frontend requests carrying modula_gallery_id parameters.
   • Inventory any private gallery content and treat its original upload URLs as potentially compromised; rotate or relocate sensitive media if capacity allows.

2. Patch / upgrade steps. No patch is currently available from the vendor or any tracked source, and no fixed version has been identified. Monitor the WordPress plugin repository and the vendor's advisory channels for a release newer than 3.0.1 that addresses the missing authorization check in Modula_Meta::add_metas(). When an update ships, treat remediation as urgent given the unauthenticated, low-complexity nature of the flaw. Validate the fix by confirming the modula_gallery_id parameter no longer yields metadata for non-public posts.

3. Long-term hardening. Adopt a least-privilege review process for WordPress plugins that register frontend hooks and accept user-controlled identifiers. Require authorization checks (current_user_can('read_post', $id)) and post-status validation before any post metadata is emitted, rather than relying on post-type checks alone. Maintain a component inventory with version tracking so affected plugins can be rapidly identified. Deploy WAF rules and web server logging capable of surfacing parameter-based enumeration, and periodically test for authorization bypasses on plugins handling media and private content.

References

• NVD — CVE-2026-89406: https://nvd.nist.gov/vuln/detail/CVE-2026-89406
• CWE-862 — Missing Authorization: https://cwe.mitre.org/data/definitions/862.html
• CVSS v3.1 Specification (FIRST.org): https://www.first.org/cvss/v3.1/specification-document
• WordPress Plugin Security — Authorization and Capability Checks (WordPress Developer Resources): https://developer.wordpress.org/plugins/security/checking-user-capabilities/
• MITRE ATT&CK — T1213, Data from Information Repositories: https://attack.mitre.org/techniques/T1213/

No threat actor campaigns or exploit-in-the-wild evidence have been reported for this CVE. It is not listed in CISA KEV, no public PoC or exploit code has been observed, and EPSS has not yet scored this vulnerability.