The Heartbleed vulnerability (CVE-2014-0160) fundamentally exploited OpenSSL's TLS/DTLS heartbeat extension implementation. While public attention focused on HTTPS, many other critical services rely on the same vulnerable OpenSSL library versions (1.0.1 through 1.0.1f).

Services vulnerable when using OpenSSL for cryptographic operations:

# Example vulnerable service detection (Debian/Ubuntu):
$ ldd $(which sshd) | grep -i openssl
    libssl.so.1.0.0 => /lib/x86_64-linux-gnu/libssl.so.1.0.0

SSH (OpenSSH): While OpenSSH uses OpenSSL, the heartbeat extension isn't implemented in SSH protocols. No direct vulnerability, but consider:

# SSH service check
$ ssh -V
OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1n  15 Mar 2022

Email Services (Dovecot/Postfix/Exim): STARTTLS implementations in SMTP/IMAP could be affected when using vulnerable OpenSSL versions for TLS handshakes.

OpenVPN's TLS-based control channel was particularly vulnerable:

# OpenVPN config check
tls-auth ta.key 0
tls-cipher TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384

Immediate actions for system administrators:

1. Update OpenSSL to 1.0.1g or later
2. Recompile services against patched OpenSSL
3. Rotate all cryptographic keys

The Heartbleed incident demonstrated the risks of shared cryptographic libraries. Modern best practices include:

• Regular dependency audits (OWASP Dependency-Check)
• Isolating crypto implementations
• Implementing certificate transparency logs

The Heartbleed vulnerability (CVE-2014-0160) fundamentally exploits a memory handling flaw in OpenSSL's TLS/DTLS heartbeat extension implementation. While most public discussions focus on HTTPS webservers, any service using vulnerable OpenSSL versions (1.0.1 through 1.0.1f) is potentially at risk.

Let's examine three critical service categories:

1. SSH Servers (sshd)

Most modern SSH implementations don't use OpenSSL's heartbeat extension by default. However:

# Check if your OpenSSH links to vulnerable OpenSSL:
ldd $(which sshd) | grep ssl
# Example remediation for Debian:
apt-get install --only-upgrade openssh-server

2. Mail Services (Dovecot/Postfix/Exim)

STARTTLS implementations in mail servers deserve special attention:

# Dovecot configuration check:
dovecot --version
# Postfix TLS status:
postconf -n | grep smtpd_tls_

3. VPN Solutions (OpenVPN)

OpenVPN's TLS-mode is particularly vulnerable:

# Verify OpenVPN linkage:
openssl version
# Emergency mitigation (until patching):
proto udp

Beyond version checking, active testing provides certainty:

# Nmap script for non-HTTP services:
nmap -sV --script ssl-heartbleed -p 22,25,465,587,993,995,1194 [target]
# Custom Python checker for proprietary ports:
import socket
import struct
def check_heartbleed(host, port):
    # ... [full implementation available in GitHub gist]

Upgrade paths vary by service:

• System-wide: apt-get upgrade openssl libssl1.0.0
• Source builds: Manual recompile against OpenSSL 1.0.1g+
• Containerized: Rebuild images with patched base layers

For systems where immediate patching isn't feasible:

# Runtime mitigation via LD_PRELOAD:
wget https://git.io/JeMYF -O heartbeat_disable.so
export LD_PRELOAD=/path/to/heartbeat_disable.so