How to Check the OpenSSL Version Number in Linux

OpenSSL is an open-source cryptographic library that provides critical security mechanisms like encryption, digital signatures, and certificates to applications and services. Knowing the specific OpenSSL version running on your Linux systems is important for ensuring security, stability, and compatibility.

In this comprehensive guide, we will explore the key methods to check OpenSSL versions on Linux, analyze why having an up-to-date version matters, delve into the meaning of OpenSSL release numbering, and cover best practices for utilizing OpenSSL as an expert full-stack developer and Linux professional.

The Risks of Outdated OpenSSL Versions

While OpenSSL enables secure encrypted connections and transactions in everything from web servers to databases, it has had considerable vulnerabilities discovered over its long history. Outdated OpenSSL versions expose organizations to weaknesses like Heartbleed in 2014 that could let attackers read sensitive data from memory.

More recently, issues like heap-based buffer overflow errors could enable denial-of-service attacks by crashing applications depending on older OpenSSL versions. Keeping OpenSSL updated is considered a security best practice to mitigate risks, especially as new cryptographic cracking methods emerge.

Below are examples of severe recent OpenSSL vulnerabilities and the recommended upgraded versions:

OpenSSL Vulnerability	Date Reported	Recommended Version
Heap-based buffer overflow	Sept 2022	>= 1.1.1s
Infinite loop DoS attack	March 2022	>= 1.1.1n

Best practice is to upgrade OpenSSL versions within a month of new releases that patch high and moderate-level vulnerabilities. Enterprises should have automated alerts in place as well.

Understanding OpenSSL Versioning

Let‘s break down the meaning behind OpenSSL version numbers, which typically follow the format of X.Y.Z:

X – The major version number, incremented for significant architectural changes that break backwards compatibility

Y – The minor version number, incremented on major new features or significant functional changes

Z – The patch number, incremented for small bug fixes or security patches

Here is a brief history of the major OpenSSL releases:

OpenSSL 1.1.x – Introduced January 2016, included major rewrite of core architecture for performance and security. Not backwards compatible.

OpenSSL 1.0.x – Introduced March 2010, massive redesign, not compatible with 0.9.x branch.

OpenSSL 0.9.x – Legacy branch from original SSLeay library, discontinued December 2019.

This background provides context on why upgrading major versions require application changes, while minor versions may only require recompilation. Tracking patches is key for security.

Comparing OpenSSL Adoption By Linux Distribution

The supported OpenSSL version can vary across Linux server distributions Even Long Term Support (LTS) distributions can lag behind latest releases. Here is a comparison of the default OpenSSL within popular distributions:

Distribution	Code Name	Release Date	OpenSSL Version
Ubuntu	22.04 LTS	April 2022	1.1.1n
Debian	11 Bullseye	August 2021	1.1.1n
RHEL	8.7	May 2022	1.1.1k
CentOS Stream	9	April 2022	3.0

As shown above, CentOS Stream 9 actually defaults all the way to OpenSSL 3.0, while RHEL 8 is still on the 1.1.1k branch from 2019. These differences can cause compatibility issues or missing out on the latest security enhancements.

Step-by-Step Guide to Checking OpenSSL Version

Now let‘s explore the recommended methods for checking your current OpenSSL version from the Linux command line:

1. openssl version

The most basic OpenSSL version check is:

openssl version

Example output:

OpenSSL 1.1.1f  31 Mar 2022

This prints out the currently installed OpenSSL version.

Breaking down an example version number 1.1.1f:

• 1 – Major release branch
• 1 – Minor release
• 1 – Patch release
• f – Patch bug-fix letter indicator

2. openssl version -a

To get the full details on the OpenSSL build information, use the -a flag:

openssl version -a

Sample output:

OpenSSL 1.1.1k  25 Mar 2021
built on: Mon Apr 20 11:53:25 2022 UTC
platform: linux-x86_64  
options:  bn(64,64) rc4(16x,int) des(int) blowfish(ptr)
compiler: gcc -I. -I.. -I../include  -fPIC -DOPENSSL_PIC -DOPENSSL_THREADS -D_REENTRANT -DDSO_DLFCN -DHAVE_DLFCN_H
OPENSSLDIR: "/usr/lib/ssl"
ENGINESDIR: "/usr/lib64/engines-1.1"

This contains additional context like the build date, target platform, enabled cryptographic options, and relevant directory paths.

3. Query Package Manager

If OpenSSL was installed from default system packages rather than source compilation, you can check with tools like YUM or APT:

apt show openssl

yum info openssl

This will reveal the OpenSSL package version for the OS distribution.

Verifying Functionality After OpenSSL Upgrades

After upgrading OpenSSL either via packages or recompiling, best practice is to thoroughly functionality test connectivity and operations depending on OpenSSL:

• Test TLS/SSL enabled services by connecting clients and examining certificate exchanges are still valid. Watch for errors about unsupported protocol versions

• For applications that utilize OpenSSL libraries, test all critical functionality and APIs after upgrade

• Use tcpdump or OpenSSL‘s s_client mode to validate expected encryption ciphers are active

• Check for Logs errors related to OpenSSL or its cryptographic operations

Automating OpenSSL Version Checks and Upgrades

Since keeping OpenSSL regularly updated is so critical for security, ops teams should consider automation:

• Schedule cron jobs to run openssl version checks monthly and email results
• Run continuous security scanning tools like Lynis that can automatically flag outdated system libraries
• Build alerting based on public Common Vulnerabilities (CVE) announcements related to OpenSSL
• Design infrastructure as code (IaC) processes to build updated OpenSSL from source along with operating system deployments

Alternative SSL/TLS Cryptographic Libraries

While OpenSSL is the most ubiquitous SSL/TLS toolkit for the Linux ecosystem, some alternatives do exist:

LibreSSL – Originating from OpenBSD in 2014, LibreSSL was forked directly from OpenSSL 1.0.1g and aims for a simpler API and leaner code. However it lags behind OpenSSL in adoption.

GnuTLS – GnuTLS supports TLS/SSL protocols but takes a different approach using GCC compiler bindings instead of external libraries. This can create portability issues from OpenSSL.

WolfSSL – Aiming for embedded and IoT use cases, WolfSSL is smaller and faster than OpenSSL but lacks enterprise-scale tooling support. Its focus is optimized execution over configurability.

For mainstream Linux server deployments, OpenSSL remains the standard cryptographic provider for its extensive protocol support, rich API ecosystem, wide third party integration, and corporate support.

Expert Recommendations on OpenSSL Best Practices

Based on many years as a full-stack developer and Linux engineer at scale, here are my top recommendations when leveraging OpenSSL:

• Actively track patches for OpenSSL related to high and moderate security CVEs – implement upgrades to mitigate new threats within 30 days

• Validate backwards compatibility for any major OpenSSL version updates – expect breakages switching between major releases like 1.0 to 1.1

• Use the "openssl version -a" output to establish centralized visibility into OpenSSL details across environments

• Build testing pipelines to catch regressions after OpenSSL upgrades – watch for subtle changes in encryption behaviors

• Monitor TLS traffic after upgrades for failure rates, security protocol version changes, cipher mismatches

• Supplement default Linux distribution OpenSSL packages with additional self-built versions if necessary for latest features

The cryptography landscape will only intensify over coming years – both in terms of vulnerabilities and computing capabilities to exploit weaknesses. Keeping OpenSSL actively updated as part of a proactive Linux security regimen is essential for every organization.