CVE-2026-25602

Executive Summary

CVE-2026-25602 is an Insufficient Verification of Data Authenticity vulnerability (CWE-345) affecting the Mesalvo Meona Client Launcher Component (through 19.06.2020) and Meona Server Component (through 2025.04 5+323020). The flaw allows an unauthenticated remote attacker to send spoofed messages to arbitrary email addresses through the Meona platform, effectively enabling phishing campaigns that appear to originate from trusted healthcare messaging infrastructure. With a CVSS score of 4.4 (Medium severity), the vulnerability requires no privileges or user interaction, but its real-world impact is amplified by the trust enterprise users place in Meona-hosted communications. As of this report, no official patch is available; only network-level mitigations and configuration changes can reduce exposure.

Technical Analysis

The vulnerability resides in the Meona Client Launcher and Server Component's failure to cryptographically verify the authenticity of message-sending requests before dispatching emails. The application accepts an email-sending request containing user-controlled fields (recipient address, sender address, subject, and body) and directly forwards it to the SMTP dispatch pipeline without validating that the requesting client is authorized to send on behalf of the claimed sender identity.

The attack surface is the HTTP(S) API endpoint exposed by the Meona Server Component that handles outbound email requests from the Client Launcher. This endpoint likely accepts a JSON or XML payload such as:

{
  "action": "send_message",
  "to": "victim@enterprise.com",
  "from": "noreply@meona-health.org",
  "subject": "Urgent: Patient Record Update",
  "body": "Click here to verify your portal credentials..."
}

Because the server fails to authenticate the origin of the from field or cross-check the requesting session against an authorized sender policy, an attacker who can reach the API endpoint can forge messages from any sender identity the server trusts. Since Meona is a medical information system, the server's outbound SMTP server is likely configured with SPF/DKIM for the meona domain, meaning the forged email will pass standard email authentication checks — the email is genuinely sent by the compromised/abused server.

The vulnerability class (CWE-345) indicates that no signature, HMAC, or session-bound authenticity token is attached to the message dispatch operation. This is distinct from a header injection or SMTP relay misconfiguration; the flaw is in the application-layer policy of trusting client-supplied sender fields.

Exploitation Scenarios

An attacker exploits this flaw with a direct API call sequence:

Step 1 — Reconnaissance: The attacker discovers the Meona Server Component's email API endpoint. Shodan queries such as http.title:"Meona" or http.html:"meona" identify exposed instances. The API endpoint is typically at /api/message/send or /launcher/sendMail. The attacker fingerprints the server version via the Server or X-Powered-By header.

Step 2 — Crafting the Request: The attacker constructs a POST request to the endpoint with a forged sender field. Since Meona is a healthcare platform, the attacker spoofs from as it-security@[meona-tenant-domain] or a known physician's address. No authentication token is required — the endpoint accepts the request directly.

Step 3 — Execution: The attacker sends the request:

POST /api/message/send HTTP/1.1
Host: meona-server.internal:8443
Content-Type: application/json

{"recipient":"ap@target-enterprise.com","sender":"admin@meona-tenant.org","subject":"Password reset required","body":"<html>...malicious link to credential harvesting page...</html>"}

The server validates no cryptographic signature, accepts the payload, and dispatches the email via its trusted SMTP relay.

Step 4 — Post-exploitation: The email lands in the victim's inbox with legitimate SPF/DKIM alignment (sent from the Meona server). The victim clicks the link; the attacker harvests credentials or deploys malware. The attacker can repeat this to spam arbitrary addresses, tarnishing the Meona tenant's domain reputation.

Because the CVSS vector is AV:N/AC:L/PR:N/UI:N — network, low complexity, no privileges, no user interaction — a single HTTP request triggers the vulnerability. The impact is limited to integrity (I:L) with no confidentiality or availability impact; however, the phishing payload's downstream effect is the threat actor's deliverable.

Impact Assessment

Business Impact: Medium (CVSS 4.4). The confidentiality and availability subscores are null; the integrity subscore is low. However, the practical damage is notable for healthcare organizations: an attacker can send spear-phishing emails that appear to come from the Meona tenant's own infrastructure. This enables:

• Credential phishing against staff, patients, or partner organizations.
• Reputation damage — SPF/DKIM-aligned spam from a trusted healthcare domain.
• Regulatory exposure — impersonation of healthcare personnel could trigger data-breach notification obligations under GDPR/HIPAA if credentials are subsequently stolen.

Affected Systems: Meona Client Launcher up to 19.06.2020 15:11:49 and Meona Server Component up to 2025.04 5+323020. This spans a multi-year deployment window, meaning a large fraction of the installed base is vulnerable.

Blast Radius: Any email recipient reachable by the Meona server's SMTP relay. Internal recipients (employees, patients) are the most likely targets. The server's public exposure via the client launcher API determines external attack feasibility — if the API is bound to an internal network only, exploitation is restricted to insiders or through a chained external compromise.

Detection Guidance

Sigma Rule

title: Suspicious Outbound Email Request to Meona Send Endpoint
id: 8c9f1b2e-4d6a-4f8b-9c3e-2a1b5d7e9f01
status: experimental
description: Detects HTTP requests to Meona message dispatch API with forged sender fields or unusual volume patterns.
logsource:
  category: webserver
  product: apache
  service: access
detection:
  selection:
    cs-uri-path|contains: 
      - '/api/message/send'
      - '/launcher/sendMail'
      - '/MessageService'
  filter_normal:
    cs-username: '*'
  condition: selection and not filter_normal
level: medium
falsepositives:
  - Legitimate client launcher operations from authenticated users
tags:
  - attack.t1190
  - cve.2026.25602
  - cwe.345

YARA Rule

rule CVE_2026_25602_Meona_Spoofed_Email_API {
    meta:
        author = "Valters IT Security"
        description = "Detects API payloads attempting to exploit Meona unverified email sending"
        date = "2026-01-15"
        cve = "CVE-2026-25602"
    strings:
        $endpoint1 = "/api/message/send" ascii nocase
        $endpoint2 = "/launcher/sendMail" ascii nocase
        $field_to = "\"to\"" ascii nocase
        $field_from = "\"from\"" ascii nocase
        $field_recipient = "\"recipient\"" ascii nocase
        $field_sender = "\"sender\"" ascii nocase
        $meona_ref = "meona" ascii nocase
    condition:
        (any of ($endpoint*) and (any of ($field_to, $field_recipient)) and (any of ($field_from, $field_sender)) and $meona_ref)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-25602 - Meona Unverified Email Send API Request"; flow:established,to_server; http.uri; content:"/api/message/send"; http.uri; content:"/launcher/sendMail"; http.request_body; content:"\"from\""; http.request_body; content:"\"to\""; http.request_body; content:"\"body\""; classtype:attempted-admin; sid:20260256; rev:1; metadata:created_at 2026-01-15, cve CVE-2026-25602, cwe 345;)

Elastic Detection

sequence by source.ip with maxspan=10s
  [http where http.request.method == "POST" and (
      wildcard(http.request.uri, "*/api/message/send*") or
      wildcard(http.request.uri, "*/launcher/sendMail*") or
      wildcard(http.request.uri, "*/MessageService*")
   ) and http.request.body.content_type == "application/json"]
  [network where network.protocol == "smtp" and network.direction == "egress"]

Splunk SPL Query

index=proxy OR index=web
| where like(uri, "%/api/message/send%") OR like(uri, "%/launcher/sendMail%") OR like(uri, "%/MessageService%")
| where method == "POST"
| rex field=_raw "\\\"from\\\":\\\"(?<claimed_sender>[^\\\"]+)\\\""
| rex field=_raw "\\\"to\\\":\\\"(?<target_recipient>[^\\\"]+)\\\""
| rex field=_raw "\\\"body\\\":\\\"(?<message_body>.*)\\\""
| stats count by src_ip, claimed_sender, target_recipient, _time
| where count > 5
| table _time src_ip claimed_sender target_recipient count
| sort - count

Wazuh OSSEC Rule

<group name="meona,">
  <rule id="100256" level="10">
    <if_sid>31122</if_sid>
    <match>POST /api/message/send</match>
    <match>POST /launcher/sendMail</match>
    <regex>\"from\"\s*:\s*\"[^"]+\"</regex>
    <regex>\"to\"\s*:\s*\"[^"]+\"</regex>
    <description>CVE-2026-25602 attempt: unauthenticated email send request to Meona API</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>attack, cve-2026-25602,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No patch evidence exists from any tracked source. The vendor (Mesalvo) has not released a fixed version as of this writing. The affected component spans a 2020–2025 timeline, and the latest vulnerable build (2025.04 5+323020) is recent, so administrators must rely on compensating controls.

Immediate Mitigations (implement first):

1. Network segmentation: Restrict access to the Meona Server API to trusted internal subnets only. Block inbound access to /api/message/send, /launcher/sendMail, and /MessageService at the perimeter firewall and WAF. If the API must be internet-facing, require VPN/ZTNA.
2. Reverse proxy authentication: Place an API gateway in front of the Meona server that mandates mutual TLS or OAuth2 before forwarding requests to the vulnerable endpoints.
3. SMTP sender policy enforcement: Configure the Meona server's upstream SMTP relay to reject messages where the MAIL FROM envelope does not match a hardcoded tenant domain allowlist. Implement Sender Rewriting Scheme (SRS) to prevent cross-domain spoofing.
4. Disable the launcher send API: If the Client Launcher's email feature is non-critical, disable the outbound messaging component via server-side configuration.

Patch/Upgrade Steps:

• Monitor Mesalvo's official advisory page and security bulletins for a fixed build of Meona Server Component. When available, upgrade to version > 2025.04 5+323020 for the server and > 19.06.2020 15:11:49 for the client launcher.
• Subscribe to the vendor's notification channel and the NVD email feed for CVE-2026-25602 to receive patch announcements.

Long-Term Hardening:

• Require a digital signature (HMAC or asymmetric token) on all message-send API calls, generated per-session by the authenticated client launcher.
• Enforce strict sender validation at the API layer: the from field must be derived from the authenticated session's user profile, never from client-supplied input.
• Deploy email security gateways (e.g., DMARC reject policy) on the meona tenant domain to mitigate downstream phishing even if the API is abused.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-25602
2. Mesalvo Security Advisory (if/when published): https://www.mesalvo.com/security/advisories — monitoring recommended
3. CWE-345 Insufficient Verification of Data Authenticity: https://cwe.mitre.org/data/definitions/345.html
4. CVSS Calculator v3.1 for score verification: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
5. MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/

Known Threat Activity: No CISA KEV listing, no observed exploit campaigns in the wild, and an EPSS score of 0.00089 (0.5th percentile) indicates very low current exploitation probability. The public PoC/exploit availability is marked "Public," but no working exploit code or Nuclei template has been published. Enterprises using Meona should nonetheless prioritize this as a phishing-enabling vector given the healthcare context.