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BEAST Attack on TLS 1.0/SSL 3.0

BEAST Attack on TLS 1.0/SSL 3.0

Description

This vulnerability indicates that the server is susceptible to BEAST attacks, which exploit predictable initialization vectors in TLS 1.0 and SSL 3.0 CBC mode encryption to recover plaintext data through blockwise chosen boundary attacks.

BEAST (Browser Exploit Against SSL/TLS) occurs when TLS 1.0 or SSL 3.0 implementations use the last ciphertext block as the initialization vector for the next record, making encryption predictable. Attackers can exploit this through JavaScript-based chosen plaintext injection to guess secrets one byte at a time.

How It Works:

  1. Attacker establishes man-in-the-middle position on network traffic
  2. Malicious JavaScript injects chosen plaintext with controlled block boundaries
  3. Predictable initialization vectors allow verification of guessed bytes
  4. Gradual extraction of sensitive data like session cookies and CSRF tokens

Requirements:

  • TLS 1.0 or SSL 3.0 with CBC cipher suites
  • Man-in-the-middle network access
  • JavaScript execution capability in the victim's browser
  • Same-origin requests to the target application

Example Scenario: A web application uses TLS 1.0 with AES-CBC encryption. An attacker on the same network injects JavaScript that makes thousands of crafted HTTPS requests, exploiting predictable IVs to guess session cookie values one byte at a time. The extracted session cookie allows complete account impersonation.

The attack demonstrates fundamental weaknesses in older TLS implementations, leading to session hijacking, authentication bypass, and potential regulatory compliance violations.

Recommendation

To mitigate BEAST attacks:

Primary Defense - Upgrade TLS Version:

# Nginx configuration - disable TLS 1.0
ssl_protocols TLSv1.2 TLSv1.3;
# Apache configuration - disable TLS 1.0/SSL 3.0
SSLProtocol -all +TLSv1.2 +TLSv1.3

Alternative Mitigations if TLS 1.0 Required:

  • Use Record Splitting: Enable empty fragment insertion (OpenSSL default)
  • Prefer Non-CBC Ciphers: Use stream ciphers or AEAD modes temporarily
  • Enable 1/n-1 Record Splitting: Browser-based countermeasure for legacy support

Testing Commands:

# Test for TLS 1.0 support
openssl s_client -connect example.com:443 -tls1

# Check cipher suites
nmap --script ssl-enum-ciphers -p 443 example.com

By upgrading to TLS 1.2+ or implementing record splitting countermeasures, organizations can effectively eliminate BEAST attack vectors while maintaining backward compatibility where necessary.

Standards

  • SOC2_CONTROLS:
    • CC_6_7
    • CC_7_1
  • CCPA:
    • CCPA_1798_150
  • GDPR:
    • ART_32
  • PCI_STANDARDS:
    • REQ_4_1
    • REQ_6_2
    • REQ_11_3