CVE-2023-49570

Executive Summary

CVE-2023-49570 identifies a critical flaw in Bitdefender Total Security’s HTTPS scanning functionality. The software improperly trusts a certificate issued by an entity that is not authorized to issue certificates, specifically when the certificate’s “Basic Constraints” extension marks it as an “End Entity” rather than a Certificate Authority (CA). This misconfiguration allows an attacker to perform a Man-in-the-Middle (MITM) attack, intercepting and potentially altering encrypted communications between the user and legitimate websites. The vulnerability undermines the trust model of HTTPS scanning, as the security product itself becomes the vector for compromise. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch or official advisory.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder or unassigned value. Based on the vulnerability description, a reasonable assessment would be:

• Attack Vector (AV): Network (N) – The attacker can exploit this remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Changed (C) – The impact extends beyond the vulnerable component.
• Confidentiality (C): High (H) – Full disclosure of encrypted traffic.
• Integrity (I): High (H) – Data can be modified in transit.
• Availability (A): None (N) – No impact on availability.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
Estimated Score: 9.1 (Critical)

Threat Level: Critical – The vulnerability allows full compromise of HTTPS traffic, enabling credential theft, data exfiltration, and injection of malicious content.

Deep Dive & Mechanics

The vulnerability resides in Bitdefender Total Security’s HTTPS scanning (SSL/TLS inspection) feature. This feature intercepts encrypted traffic by acting as a proxy, decrypting and re-encrypting data to scan for threats. To do this, the software generates or trusts a local CA certificate that is installed in the system’s trust store.

The flaw occurs when the software trusts a certificate that has the “Basic Constraints” extension set to “End Entity” (i.e., CA:FALSE). In a proper PKI hierarchy, only CA certificates (with CA:TRUE) should be trusted to issue other certificates. By trusting an end-entity certificate as a CA, Bitdefender allows an attacker who can present such a certificate to impersonate any website. This could happen if:

• An attacker compromises the local certificate store.
• An attacker uses a malicious application to install a crafted certificate.
• The software incorrectly validates certificates during the scanning process.

The impact is a classic MITM scenario: the attacker can decrypt, read, and modify all HTTPS traffic passing through the Bitdefender proxy, including login credentials, session tokens, and sensitive data.

Vulnerable vs. Patched Code

No specific code snippets are available for this CVE. However, the vulnerable behavior can be described conceptually:

Vulnerable Code (Conceptual):

// Pseudocode for certificate validation in HTTPS scanning
if (certificate.IsTrusted()) {
    // Trust the certificate without checking Basic Constraints
    AcceptCertificate(certificate);
}

Patched Code (Conceptual):

// Patched validation
if (certificate.IsTrusted() && certificate.BasicConstraints == CA_TRUE) {
    AcceptCertificate(certificate);
} else {
    RejectCertificate(certificate);
}

The fix would involve ensuring that only certificates with the CA:TRUE Basic Constraints extension are trusted as issuers. Without a vendor patch, users must rely on workarounds.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A machine running Bitdefender Total Security with HTTPS scanning enabled.
• Ability to install a custom root CA certificate on the target system (e.g., via social engineering or local access).
• A tool like mitmproxy or BetterCAP to perform the MITM attack.

Steps:

1. Generate a self-signed certificate with BasicConstraints=CA:FALSE (end-entity) but mark it as a CA in the trust store.
2. Install this certificate into the system’s trusted root store.
3. Configure the MITM tool to use this certificate for all HTTPS connections.
4. Route traffic through the MITM proxy (e.g., by ARP spoofing or DNS poisoning).
5. Observe decrypted traffic in real-time.

Example mitmproxy command:

mitmproxy --mode transparent --listen-port 8080 --set block_global=false --certs *=malicious.pem

Blue Team (Defense & Detection)

Detection Steps:

• Monitor for unexpected certificate installations in the system trust store.
• Use certificate transparency logs to detect rogue certificates.
• Enable logging on Bitdefender to capture certificate validation failures.
• Deploy network monitoring to detect MITM indicators (e.g., certificate mismatches, unexpected CA issuers).

Mitigation:

• Disable HTTPS scanning in Bitdefender until a patch is available.
• Use a separate, trusted proxy for SSL inspection.
• Implement certificate pinning for critical services.

Indicators of Compromise (IOCs)

• Certificate Fingerprint: Any certificate with BasicConstraints: CA:FALSE that is trusted by Bitdefender’s HTTPS scanning.
• Network Traffic: Unusual SSL/TLS handshake patterns, such as certificates issued by unexpected CAs.
• System Events: Event ID 64 (Certificate Services) or similar logs indicating installation of a new root CA.
• File Hashes: Malicious certificate files (.pem, .crt, .p12) with suspicious metadata.

Detection Engineering

YARA Rule

rule Detect_Malicious_Certificate_BasicConstraints {
    meta:
        description = "Detects certificates with BasicConstraints CA:FALSE that may be used for MITM"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-49570"
    strings:
        $basic_constraints = "Basic Constraints" nocase
        $ca_false = "CA:FALSE" nocase
        $end_entity = "End Entity" nocase
    condition:
        $basic_constraints and ($ca_false or $end_entity)
}

Sigma Rule

title: Suspicious Certificate Installation for MITM
id: 8f4a3b2c-1d5e-4f6a-8b7c-9d0e1f2a3b4c
status: experimental
description: Detects installation of certificates with BasicConstraints CA:FALSE that could be used for MITM attacks (CVE-2023-49570)
author: Valters IT
logsource:
    product: windows
    service: security
    category: certificate_services
detection:
    selection:
        EventID: 64
        CertificateSubject: "*"
        CertificateIssuer: "*"
    condition: selection
falsepositives:
    - Legitimate certificate updates
level: high

Suricata Rule

alert tls any any -> any any (msg:"CVE-2023-49570 - Suspicious Certificate BasicConstraints"; flow:to_server; tls.cert_issuer; content:"Basic Constraints"; nocase; pcre:"/CA:FALSE|End Entity/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable HTTPS Scanning: Temporarily turn off the HTTPS scanning feature in Bitdefender Total Security to prevent exploitation.
2. Monitor Certificates: Audit the system’s trusted root certificates for any unauthorized or suspicious entries.
3. Update Software: Check for any pending updates from Bitdefender. If no patch is available, consider using an alternative security solution.

Long-Term Fix:

• Wait for an official patch from Bitdefender that properly validates the Basic Constraints extension.
• Implement certificate pinning for critical internal services.
• Use a dedicated, properly configured SSL inspection proxy.

Workaround:

• If HTTPS scanning must remain enabled, restrict the trusted CA list to only known, authorized CAs.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert