Every encrypted connection your application makes depends on a TLS library. The choice of which library to use is one of the highest-impact security decisions in your stack, yet most teams inherit whatever their framework or operating system provides without a second thought.
The major options -- OpenSSL, BoringSSL, LibreSSL, and rustls -- have fundamentally different design philosophies, security track records, and trade-offs. Understanding them matters.
OpenSSL
OpenSSL is the default TLS library on most Linux distributions and powers the majority of HTTPS traffic on the internet. It is comprehensive, supporting nearly every cipher suite, protocol version, and extension in the TLS specification.
Strengths. Universal compatibility. If you need to connect to old or obscure systems, OpenSSL will support whatever cipher suite they require. It has extensive documentation, a large contributor base, and FIPS 140-2/3 validated configurations for regulated environments.
Weaknesses. The codebase is enormous and complex. OpenSSL has had a long history of severe vulnerabilities, the most notorious being Heartbleed (CVE-2014-0160), which exposed server memory to remote attackers. The API is notoriously difficult to use correctly -- setting up a TLS connection with proper certificate verification requires careful attention to dozens of configuration options.
Security track record. After Heartbleed, OpenSSL received significant investment through the Core Infrastructure Initiative. Code quality has improved substantially. However, the fundamental issue remains: OpenSSL is written in C, supports every feature in the TLS specification, and has a massive attack surface.
BoringSSL
BoringSSL is Google fork of OpenSSL, created in 2014. Google maintains it for use in Chrome, Android, and their internal infrastructure.
Strengths. BoringSSL strips out features that Google considers unnecessary or dangerous. It does not support SSL 3.0, removed support for weak cipher suites early, and has a smaller codebase than OpenSSL. Google continuous fuzzing infrastructure exercises BoringSSL extensively.
Weaknesses. BoringSSL is not intended for general use. Google explicitly states that they do not guarantee API stability, provide release versions, or support external users. If you adopt BoringSSL, you are on your own for packaging, versioning, and compatibility.
Security track record. BoringSSL has had significantly fewer CVEs than OpenSSL, partly because of its smaller feature set and partly because of Google investment in testing. However, it shares some historical code with OpenSSL, so it is not immune to bugs that originate in the shared codebase.
LibreSSL
LibreSSL is the OpenBSD fork of OpenSSL, created after Heartbleed. The OpenBSD team aggressively removed legacy code, unsafe patterns, and unnecessary features.
Strengths. Significant code cleanup. LibreSSL removed hundreds of thousands of lines of code from OpenSSL, including support for obsolete platforms, deprecated protocols, and dangerous features. The codebase is cleaner and more auditable.
Weaknesses. LibreSSL has had compatibility issues with software that depends on OpenSSL-specific APIs. Some Linux distributions tried to use LibreSSL as a drop-in replacement and encountered problems. It has a smaller development team than OpenSSL.
Security track record. LibreSSL has had fewer CVEs than OpenSSL, but it has also received less security research attention. The OpenBSD team applies rigorous coding standards, but the library has not been fuzzed as extensively as OpenSSL or BoringSSL.
rustls
rustls is a TLS library written in Rust. It uses the ring cryptographic library (which wraps BoringSSL assembly for performance-critical operations) and provides a memory-safe TLS implementation.
Strengths. Memory safety by construction. The entire class of vulnerabilities that has plagued OpenSSL -- buffer overflows, use-after-free, double-free -- cannot occur in rustls safe Rust code. The API is designed to be difficult to misuse. rustls does not support known-insecure protocol versions or cipher suites.
Weaknesses. rustls does not support every TLS feature. Some legacy cipher suites and protocol extensions are deliberately excluded. If you need to connect to old systems that only support TLS 1.0 or export-grade ciphers, rustls will not help. It also requires the Rust toolchain, which may not be available or desirable in every environment.
Security track record. rustls has had very few CVEs, and none of them involved memory corruption. The bugs that have been found are logic issues, not the catastrophic memory safety failures that characterize OpenSSL history.
Making the Choice
For most new projects: rustls is the best choice if your technology stack supports it. The memory safety guarantees eliminate the most common and most severe class of TLS vulnerabilities.
For regulated environments: OpenSSL with FIPS validation may be required. Check your compliance requirements before choosing.
For maximum compatibility: OpenSSL supports everything. If you need to interoperate with legacy systems, it is the pragmatic choice.
For Google-ecosystem projects: BoringSSL integrates naturally with Google tooling and infrastructure.
For security-focused projects without Rust: LibreSSL offers a cleaner, leaner alternative to OpenSSL for C-based projects.
Regardless of which library you choose, keep it updated. TLS library vulnerabilities are among the most impactful in the entire software ecosystem.
How Safeguard.sh Helps
Safeguard.sh tracks TLS library versions across your entire application portfolio. Whether your applications use OpenSSL, BoringSSL, LibreSSL, or rustls, our platform monitors for CVEs, identifies end-of-life versions, and provides remediation guidance. Our SBOM generation captures TLS dependencies that are often invisible in application-level package manifests, ensuring complete visibility into one of the most critical components of your security infrastructure.