CVE-2023-49567

Executive Summary

CVE-2023-49567 identifies a critical flaw in Bitdefender Total Security's HTTPS scanning functionality. The vulnerability stems from the product's failure to properly validate SSL/TLS certificates, specifically trusting certificates issued using the weak MD5 and SHA1 collision hash functions. This allows an attacker to perform a Man-in-the-Middle (MITM) attack by presenting a rogue certificate that appears legitimate, thereby intercepting and potentially modifying encrypted traffic to any arbitrary site. The vulnerability has a CVSS score of 0.0 (likely unassigned or pending), but the technical impact is severe, as it undermines the core security promise of HTTPS scanning. No public exploit code or proof-of-concept is currently available, but the weakness is well-understood in cryptographic circles.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is atypical and may indicate that the score has not been officially assigned or is pending review. Based on the vulnerability description, a reasonable estimated CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The attacker can be remote.
• Attack Complexity (AC): Low (L) – Exploiting weak hash collisions is well-documented.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – The victim does not need to perform any action.
• Scope (S): Unchanged (U) – The vulnerable component is the HTTPS scanner.
• Confidentiality (C): High (H) – Full traffic decryption possible.
• Integrity (I): High (H) – Traffic can be modified.
• Availability (A): Low (L) – No direct DoS, but service disruption possible.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L Estimated Score: 8.6 (High)

Threat Level: High. The vulnerability allows an attacker to bypass HTTPS security, intercept sensitive data (credentials, personal information), and inject malicious content into encrypted streams.

Deep Dive & Mechanics

The vulnerability lies in Bitdefender Total Security's HTTPS scanning (SSL/TLS inspection) feature. This feature is designed to decrypt and inspect encrypted traffic for malware, but it must re-encrypt the traffic using a trusted certificate. The flaw is that the product accepts certificates signed with MD5 or SHA1 hash functions, which are known to be vulnerable to collision attacks.

• MD5 Collision Attack: An attacker can generate two different certificates with the same MD5 hash. One certificate is legitimate (e.g., for a benign site), and the other is rogue (e.g., for a malicious site). The attacker presents the rogue certificate to the Bitdefender scanner, which trusts it because the hash matches a trusted root.
• SHA1 Collision Attack: Similarly, SHA1 collisions are computationally feasible (as demonstrated by the SHAttered attack). The attacker can create a rogue certificate that has the same SHA1 hash as a trusted certificate.

Attack Flow:

1. The victim's machine has Bitdefender Total Security with HTTPS scanning enabled.
2. The attacker performs a MITM attack (e.g., ARP spoofing, DNS poisoning, or rogue Wi-Fi).
3. The victim's browser attempts to connect to https://bank.com.
4. The attacker intercepts the connection and presents a rogue certificate for bank.com that is signed using MD5 or SHA1.
5. Bitdefender's HTTPS scanner validates the certificate but incorrectly accepts it because it trusts certificates with MD5/SHA1 signatures.
6. The attacker can now decrypt, view, and modify the traffic between the victim and bank.com.

Vulnerable vs. Patched Code

No specific code snippets are available from public sources. However, the vulnerability is a logic flaw in certificate validation logic.

Vulnerable (Conceptual):

// Pseudo-code for vulnerable certificate validation
bool validate_certificate(certificate_t cert) {
    if (cert.signature_algorithm == MD5 || cert.signature_algorithm == SHA1) {
        return true; // Incorrectly trusts weak hashes
    }
    // ... other validation
}

Patched (Conceptual):

// Pseudo-code for patched certificate validation
bool validate_certificate(certificate_t cert) {
    if (cert.signature_algorithm == MD5 || cert.signature_algorithm == SHA1) {
        return false; // Rejects weak hashes
    }
    // ... other validation
}

The patch would involve updating the certificate validation logic to reject certificates signed with MD5 or SHA1, and only accept those using SHA256 or stronger.

Exploitation & Lab Setup

Red Team (Attacker)

Objective: Perform a MITM attack to intercept HTTPS traffic from a victim running Bitdefender Total Security.

Tools Required:

• bettercap or mitmproxy for MITM interception.
• openssl to generate rogue certificates.
• A tool to perform MD5/SHA1 collision (e.g., hashclash for MD5, shattered for SHA1).

Lab Setup:

1. Environment: Two VMs (Attacker: Kali Linux, Victim: Windows 10 with Bitdefender Total Security).
2. Network: Both VMs on the same isolated network (e.g., NAT network in VirtualBox).

Steps:

1. Generate Rogue Certificate:

   # Generate a rogue CA certificate using MD5
   openssl req -x509 -newkey rsa:2048 -keyout rogue_ca.key -out rogue_ca.crt -days 365 -nodes -subj "/CN=RogueCA" -md5
   

2. Perform ARP Spoofing:

   # Using bettercap
   sudo bettercap -eval "set arp.spoof.targets 192.168.1.10; arp.spoof on"
   

3. Intercept and Decrypt Traffic:

   # Using mitmproxy with the rogue CA
   mitmproxy --mode transparent --listen-port 8080 --set ssl_insecure=true --certs *=rogue_ca.crt
   

4. Victim Configuration: The victim must trust the rogue CA certificate (e.g., install it in the Trusted Root Certification Authorities store). This is often done via social engineering or if the attacker has prior access.

Note: The actual exploitation requires the victim to trust the attacker's rogue CA, which is a common MITM prerequisite. The vulnerability makes this easier because Bitdefender does not reject the weak hash.

Blue Team (Defender)

Detection:

• Monitor for unexpected certificate installations in the Trusted Root store.
• Alert on the use of MD5 or SHA1 signed certificates in HTTPS scanning logs.
• Use network monitoring to detect ARP spoofing or DNS poisoning.

Prevention:

• Disable HTTPS scanning if not strictly necessary.
• Ensure Bitdefender is updated to the latest version (once a patch is available).
• Implement certificate pinning for critical services.

Indicators of Compromise (IOCs)

• Network:
  • ARP cache entries with multiple IPs for the same MAC address.
  • DNS responses pointing to unexpected IPs.
  • SSL/TLS certificates with MD5 or SHA1 signature algorithms in HTTPS scanning logs.
• Host:
  • Unexpected trusted root certificates (especially those with weak hashes).
  • Bitdefender logs showing certificate validation failures or warnings.
• File:
  • Rogue CA certificate files (e.g., rogue_ca.crt) in unusual locations.

Detection Engineering

YARA Rule

rule CVE_2023_49567_Bitdefender_Weak_Cert {
    meta:
        description = "Detects certificates signed with MD5 or SHA1 that may be used in MITM attacks against Bitdefender Total Security"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-49567"
    strings:
        $md5 = "MD5" ascii nocase
        $sha1 = "SHA1" ascii nocase
        $cert_header = "-----BEGIN CERTIFICATE-----" ascii
    condition:
        $cert_header and ($md5 or $sha1)
}

Sigma Rule

title: Detection of Weak Certificate Hash Usage in HTTPS Scanning
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects events where Bitdefender Total Security logs indicate acceptance of MD5 or SHA1 signed certificates.
author: Valters IT
date: 2025-04-10
logsource:
    product: bitdefender
    service: https_scanning
detection:
    selection:
        EventID: 1001  # Hypothetical event ID for certificate validation
        SignatureAlgorithm:
            - "MD5"
            - "SHA1"
    condition: selection
falsepositives:
    - Legitimate use of weak hashes in internal networks (rare)
level: high

Suricata Rule

alert tls any any -> any any (msg:"CVE-2023-49567 - Weak Certificate Hash (MD5/SHA1) Detected"; flow:to_server; tls.cert_issuer; content:"MD5"; nocase; sid:1000001; rev:1;)
alert tls any any -> any any (msg:"CVE-2023-49567 - Weak Certificate Hash (MD5/SHA1) Detected"; flow:to_server; tls.cert_issuer; content:"SHA1"; nocase; sid:1000002; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable HTTPS Scanning: Temporarily disable the HTTPS scanning feature in Bitdefender Total Security until a patch is applied.
   • Go to Settings > Protection > Online Threat Prevention > HTTPS Scanning > Off.
2. Update Bitdefender: Check for updates from Bitdefender. If a patch is available, apply it immediately.
3. Monitor Certificates: Review installed trusted root certificates for any that use MD5 or SHA1 signatures. Remove any suspicious ones.

Long-term Mitigation:

• Certificate Pinning: Implement certificate pinning for critical internal services to prevent MITM attacks.
• Network Segmentation: Isolate sensitive systems from untrusted networks.
• User Education: Train users to recognize social engineering attempts that install rogue certificates.

Patch Status: UNKNOWN. Contact Bitdefender support for the latest patch information.

Valters IT