OpenSSL 3.6: What's New, Release History & EOL Status

What Is New in OpenSSL 3.6

What new cryptographic capabilities does OpenSSL 3.6 bring?

OpenSSL 3.6 adds a suite of modern algorithms and key-handling primitives that were previously unavailable.

• NIST security categories are now attached to PKEY objects, enabling policy-driven key usage.
• The EVP_SKEY opaque symmetric key type lets providers expose raw key material without leaking it to the application layer.
• LMS (Leighton-Micali-Signature) verification is supported out-of-the-box, complying with SP 800-208.
• Deterministic ECDSA per FIPS 186-5 is available in the FIPS provider, useful for reproducible signatures.

Example: deriving a symmetric key with the new API:

EVP_KDF *kdf = EVP_KDF_fetch(NULL, "HKDF", NULL);
EVP_KDF_CTX *ctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_CTX_set_params(ctx, OSSL_PARAM_construct_utf8_string("digest", "SHA256", 0));
EVP_KDF_CTX_set_SKEY(ctx, NULL, 0); /* opaque key placeholder */
EVP_KDF_derive_SKEY(ctx, out, outlen);
EVP_KDF_CTX_free(ctx);
EVP_KDF_free(kdf);

How has OpenSSL 3.6 hardened its security posture?

The 3.6 series patches dozens of high-impact vulnerabilities across the TLS, CMS, PKCS#12, and low-level crypto code paths.

• RSA-KEM encapsulation failure handling (CVE-2026-31790) and AES-CFB-128 out-of-bounds read on AVX-512 CPUs (CVE-2026-28386).
• Multiple NULL-pointer dereferences in delta CRL, CMS KeyAgreeRecipientInfo, and KeyTransportRecipientInfo handling (CVE-2026-28388-28390).
• Heap buffer overflow in hex conversion (CVE-2026-31789) and in PKCS#12 friendly-name UTF-8 conversion (CVE-2025-69419).
• Fixes for TLS 1.3 compressed certificate memory blow-up (CVE-2025-66199) and DANE client use-after-free (CVE-2026-28387).

In practice these patches eliminate denial-of-service vectors and prevent potential key-material leakage in production workloads.

What breaking changes and deprecations should I watch for when moving to OpenSSL 3.6?

Upgrading to 3.6 requires attention to removed platform support, compiler requirements, and API deprecations.

• VxWorks support removed - any embedded build targeting VxWorks must migrate to a supported OS.
• C-99 compiler required - the build now uses designated initializers and other C-99 features; older ANSI-C toolchains will fail.
• EVP_PKEY_ASN1_METHOD functions deprecated - replace calls such as EVP_PKEY_asn1_find_str() with provider-based lookups like EVP_PKEY_new() and EVP_PKEY_get0().

Example migration snippet:

// Old API (deprecated)
EVP_PKEY_ASN1_METHOD *ameth = EVP_PKEY_asn1_find_str(NULL, "RSA", -1);
// New API
EVP_PKEY *pkey = EVP_PKEY_new();
EVP_PKEY_set_type(pkey, EVP_PKEY_RSA);

What new tooling does OpenSSL 3.6 provide for configuration management?

The openssl configutl utility helps operators validate and dump the effective OpenSSL configuration.

• Parses the standard openssl.cnf file and resolves includes, defaults, and environment substitutions.
• Outputs a normalized, human-readable representation that can be diffed against previous versions.
• Useful for CI pipelines to ensure configuration drift is caught early.

Typical usage:

openssl configutl -dump -config /etc/ssl/openssl.cnf