OpenSSL Patches Multiple High-Severity Vulnerabilities

Key Takeaways

• OpenSSL has released patches for seven vulnerabilities, including two rated Moderate severity.
• The flaws impact multiple widely used OpenSSL versions: 4.0, 3.6, 3.5, 3.4, 3.0, and in some cases, the legacy 1.1.1 and 1.0.2 branches.
• Vulnerabilities range from heap corruption and invalid pointer dereferences to memory exhaustion issues in QUIC and DTLS.
• Many of these bugs are remotely triggerable by unauthenticated attackers, posing a significant risk to services utilizing OpenSSL for TLS, CMS, or CMP.
• Immediate patching is critical for organizations to prevent potential denial-of-service or information integrity attacks.

OpenSSL Addresses Seven Vulnerabilities Across Cryptographic Library

OpenSSL, the widely adopted cryptographic software library, has released a critical security advisory addressing seven vulnerabilities. These flaws span various components, from heap-corrupting write bugs to memory exhaustion issues within its QUIC and DTLS implementations. The affected versions include OpenSSL 4.0, 3.6, 3.5, 3.4, 3.0, and in specific instances, the older 1.1.1 and 1.0.2 lines. Organizations relying on OpenSSL for TLS, CMS, or CMP services are strongly advised to prioritize patching.

Moderate-Severity Flaws Identified

Among the disclosed vulnerabilities, two are classified as Moderate severity. The most critical, identified as CVE-2026-63072, resides within OpenSSL’s CMS decryption code. This flaw involves a heap buffer overflow during the sizing of a buffer for an unwrapped key. The AES-WRAP-PAD unwrap primitive can write and cleanse more bytes than reported by the buffer size query. Attackers can exploit this by modifying a single byte in a legitimate encrypted message’s key-wrap algorithm identifier. This manipulation forces an 8-byte out-of-bounds heap write when CMS_decrypt() is called, leading to heap corruption and a denial of service. OpenSSL notes that while reliable, the outcome is more likely a DoS than remote code execution.

The second Moderate-severity issue, CVE-2026-63076, impacts the Certificate Management Protocol (CMP). This vulnerability involves an invalid pointer dereference that occurs because OpenSSL’s password-based MAC verification only checks for a non-null protection algorithm parameter, failing to confirm its actual type. A specially crafted message can trigger this flaw, allowing a remote, unauthenticated attacker to crash a CMP server or a CMP client connecting to a malicious server.

Low-Severity Issues and Memory Exhaustion Risks

The advisory also details five Low-severity vulnerabilities, several of which pose significant risks through memory exhaustion or integrity bypasses:

• CVE-2026-14457: A null pointer dereference can occur in TLS servers or clients configured with Raw Public Keys but without a corresponding certificate, when a peer sends the signature_algorithms_cert extension. This affects OpenSSL versions 4.0, 3.6, 3.5, and 3.4.
• CVE-2026-54874: This vulnerability allows for excessive memory use by buffering DTLS records for a future epoch. Attackers can amplify network traffic by approximately 1,200 times, causing a DTLS endpoint to buffer large read buffers for small, forged records, leading to memory exhaustion on busy servers. This affects a broad range of versions, including 4.0, 3.6, 3.5, 3.4, 3.0, 1.1.1, and 1.0.2.
• CVE-2026-63073: In CMP response validation, an untrusted sender Distinguished Name (DN) is used directly as a format string in a logging function. This format string vulnerability allows a malicious CMP endpoint to crash a client through classic format-string abuse. Versions 4.0, 3.6, 3.5, and 3.4 are impacted.
• CVE-2026-63074: This flaw permits indefinite cache growth of extra certificates in CMP. Malicious clients can flood long-lived server contexts with rejected messages that are not properly cleaned up, leading to out-of-memory (OOM) conditions. Affected versions include 4.0, 3.6, 3.5, 3.4, and 3.0.
• CVE-2026-63075: Memory exhaustion in OpenSSL’s QUIC stack is possible if a peer withholds acknowledgments while forcing ACK-only packets, causing connection-scoped memory usage to inflate indefinitely. This affects OpenSSL 4.0, 3.6, 3.5, and 3.4.
• CVE-2026-75803: This issue affects AEAD ciphers ChaCha20-Poly1305 and AES-OCB. Calling EVP_Cipher() with empty ciphertext can report a successful decryption without verifying the authentication tag, potentially allowing forged messages to be accepted. This impacts OpenSSL 4.0, 3.6, 3.5, 3.4, and 3.0.

Available Patches and Mitigation

OpenSSL has released patched versions to address all identified vulnerabilities: 4.0.2, 3.6.4, 3.5.8, 3.4.7, and 3.0.22. Additionally, premium support customers on the 1.1.1 and 1.0.2 branches will receive separate backports. It is important to note that none of these flaws affect the FIPS module boundary.

What You Should Do

• Inventory OpenSSL Usage: Identify all systems and applications that use OpenSSL, particularly those running TLS, CMS, or CMP services.
• Prioritize Patching: Immediately apply the relevant patched versions (4.0.2, 3.6.4, 3.5.8, 3.4.7, 3.0.22) to all affected OpenSSL installations.
• Update Legacy Systems: For organizations with premium support, ensure that legacy 1.1.1 and 1.0.2 branches receive their respective backports.
• Monitor for Exploitation: Remain vigilant for any signs of exploitation attempts, especially denial-of-service attacks or unusual memory consumption.
• Review Configurations: Assess configurations for services that might be particularly vulnerable, such as CMP servers accepting PBM-protected messages or TLS servers with Raw Public Key setups without certificates.

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