Heartbleed Vulnerability Analysis

[Cloned Boy]

The Heartbleed vulnerability (CVE-2014-0160) is a critical vulnerability in the OpenSSL library discovered in 2014. It allows an attacker to read the contents of a server's RAM, which could lead to the leak of sensitive data, including private keys, passwords, and other sensitive information.

The essence of vulnerability​

1. TLS/SSL Protocol and Heartbeat Extension
   • OpenSSL implements the TLS/SSL encryption protocols used to secure Internet connections.
   • The Heartbeat extension allows you to check if a remote server is alive by sending a small request and waiting for a response.
2. Error processing Heartbeat request
   • The vulnerability was in the dtls1_process_heartbeat() (for DTLS) and tls1_process_heartbeat() (for TLS) functions.
   • The server did not correctly validate the length (payload_length) in the Heartbeat request.
   • An attacker could send a request with a small actual payload (e.g. 1 byte), but specify a large length (up to 64 KB).
   • In response, the server copied not only the transmitted data, but also random data from its memory corresponding to the specified length.

Technical details​

• Affected OpenSSL versions: 1.0.1 – 1.0.1f (fixed in 1.0.1g).
• Attack type: Read Overflow.
• Possible consequences:
  • Server private keys leaked.
  • Session interception (cookies, tokens).
  • Compromise of user data.

Example request (simplified):

| type (1B) | payload_length (2B) | payload (N bytes) | padding |

If payload_length = 65535 and the actual payload = "A" (1 byte), the server will return "A" + 65534 bytes from memory.

Vulnerability code (before fix)​

/* Vulnerable code in OpenSSL (simplified) */
memcpy(bp, pl, payload_length); // Copy payload + data from memory

Fix :
Added check that payload_length matches the actual payload length.

How was the vulnerability exploited?​

1. The attacker sent a specially crafted Heartbeat request.
2. The server responded by including random data from its memory in the response.
3. By repeating requests, it was possible to obtain critical information (such as TLS private keys).

Example of using the openssl utility to check for vulnerability:

openssl s_client -connect example.com:443 -tlsextdebug 2>&1 | grep "TLS server extension"

If the server supported Heartbeat, it could be vulnerable.

Consequences and scale​

• Thousands of servers are affected (including large companies like Yahoo, Cloudflare).
• The vulnerability existed for 2 years before being discovered.
• A massive replacement of SSL certificates was required.

Protective measures​

1. Update OpenSSL to version 1.0.1g or later.
2. Disable the Heartbeat extension if you don't need it.
3. Replace SSL certificates after a potential leak.
4. Use IDS/IPS to detect abnormal Heartbeat requests.

Conclusion​

Heartbleed is one of the most dangerous vulnerabilities in the history of the Internet, which showed the importance of auditing open-source libraries. It led to stricter security practices and a more careful approach to checking cryptographic code.

 

[hackito]

Heartbleed (CVE-2014-0160) was a critical vulnerability in OpenSSL (versions 1.0.1–1.0.1f) caused by improper input validation in the Heartbeat extension. Attackers could exploit it to read up to 64KB of server memory per request, exposing sensitive data like private keys and passwords. It was exploited via malformed Heartbeat requests, triggering memory leaks. The fix involved checking that the payload length matched the actual data length. Heartbleed highlighted the need for rigorous security auditing, especially in cryptographic libraries, and led to widespread certificate revocation and updated security practices across the internet.