CVE-2023-5363

What it actually does

Bug in EVP_EncryptInit_ex2, EVP_DecryptInit_ex2 and EVP_CipherInit_ex2 causes OSSL_PARAM keylen/ivlen changes to be ignored after key/IV setup, resulting in IV truncation or key/IV overruns for RC2/RC4/RC5/CCM/GCM/OCB, producing non-unique IVs or incorrect cipher output that can leak confidentiality in GCM/CCM/OCB modes.

Why it matters to the business

Rare but serious risk of confidentiality loss in applications performing dynamic key or IV length changes with affected symmetric ciphers; low likelihood due to uncommon usage pattern and recent API introduction reduces operational urgency despite 1086 days of exposure.

How an attack unfolds

An attacker identifies an application that calls the vulnerable EVP_*Init_ex2 functions with OSSL_PARAM arrays altering keylen or ivlen after initial setup, supplies crafted parameters that cause IV truncation (especially in deterministic GCM constructions), and observes resulting IV reuse or decryption failures to recover plaintext.

How to fix it

Upgrade OpenSSL to the fixed commit c3cc0f1386b0544383a61244a4beeb762b67498f or later; rebuild and redeploy all dependent applications and libraries; avoid dynamic key/IV length changes via OSSL_PARAM until patched.

How to confirm the fix worked

Confirm OpenSSL library version or commit contains c3cc0f1386b0544383a61244a4beeb762b67498f; run regression tests exercising EVP_*Init_ex2 with keylen/ivlen OSSL_PARAM on affected ciphers and verify correct IV/key lengths are applied.

Typical attack path

1. Locate application using OpenSSL 3.0/3.1 with CCM/GCM/OCB or legacy RC ciphers that dynamically sets key/IV lengths via OSSL_PARAM
2. Trigger calls to EVP_EncryptInit_ex2 or equivalent with malicious keylen/ivlen parameters
3. Induce IV truncation leading to reuse or overread conditions
4. Decrypt or observe ciphertext to compromise confidentiality

How to detect it

Review application logs for cipher initialization errors, decryption failures, or unexpected IV reuse warnings when using affected modes; inspect source for calls to EVP_*Init_ex2 followed by keylen or ivlen OSSL_PARAM; no public exploitation artifacts reported.

What your security team should do

• Inventory all OpenSSL 3.0 and 3.1 deployments and flag any use of CCM/GCM/OCB or RC ciphers with dynamic length parameters
• Apply the fix commit c3cc0f1386b0544383a61244a4beeb762b67498f or newer releases immediately on internet-facing or high-value systems
• Update build pipelines and dependency manifests to enforce the patched version
• Monitor EPSS and KEV status for any future increase in exploitation likelihood