On January 27, 2026, OpenSSL fixed 12 vulnerabilities, one of which was a high-severity flaw that could cause remote code execution This article explores extremely dangerous openssl. . The majority of problems lead to denial-of-service attacks, but they also draw attention to the dangers of parsing untrusted data.

CVE-2025-15467, the most significant vulnerability, affects CMS AuthEnvelopedData parsing using AEAD ciphers such as AES-GCM. Before authentication checks, attackers create oversized IVs in ASN.1 parameters, resulting in stack overflows. Applications handling untrusted CMS or PKCS#7 data, like S/MIME, may crash or execute remote code as a result. Since no key is required to initiate the overflow, apps that parse remote CMS content are at high risk.

Platform defenses like ASLR are necessary for exploitability, but the stack write primitive is extremely dangerous. OpenSSL gave it a high severity rating.

In PKCS#12 files, CVE-2025-11187 involves incorrect PBMAC1 validation that causes null dereferences or stack overflows in versions 3.6 to 3.4. If the length of the key exceeds 64 bytes, malicious files cause buffer overflows during key derivation. PKCS#12 handling was also affected by a number of low-severity issues, such as CVE-2025-69419, CVE-2025-69421, and CVE-2026-22795, which resulted in null derefs or out-of-bounds writes.

Versions Affected by CVE ID Severity Brief Impact CVE-2025-11187 Patched Versions PKCS#12 MAC 3.6, 3.5, 3.4, 3.6.1, 3.5.5, 3.4.4 CVE-2025-15467 has a moderate stack overflow. CMS parsing with a high stack overflow CVE-2025-15468 3.6-3.0 3.6.1, 3.5.5, 3.4.4, 3.3.6, 3.0.19 Low Null deref in QUIC cipher lookup 3.6, 3.5, 3.4, 3.3, 3.6.1, 3.5.5, 3.4.4, 3.3.6 CVE-2025-15469 Large inputs are truncated by the low dgst tool CVE-2025-66199 3.6, 3.5, 3.6.1, and 3.5.5 Low compression of TLS 1.3 certificates DoS 3.6, 3.5, 3.4, 3.3 3.6.1, 3.5.5, 3.4.4, 3.3.6 CVE-2025-68160 Minimal Heap OOB write in the linebuffer of BIO 3.6-3.0, 1.1.1, 1.0.2 3.6.1-3.0.19, 1.1.1ze, 1.0.2zn CVE-2025-69418 Low OCB tail bytes unencrypted 3.6-3.0, 1.1.1 3.6.1-3.0.19, 1.1.1ze CVE-2025-69419 Low OOB write in PKCS12 friendlyname 3.6-3.0, 1.1.1 3.6.1-3.0.19, 1.1.1ze CVE-2025-69420 Low Null deref in timestamp verify 3.6-3.0, 1.1.1 3.6.1-3.0.19, 1.1.1ze CVE-2025-69421 Low PKCS12 decrypt 3.6-3.0, 1.1.1, 1.0.2, 3.6.1-3.0.19, 1.1.1ze, 1.0.2zn CVE-2026-22795 null deref PKCS#12 3.6-3.0, 1.1.1 3.6.1-3.0.19, 1.1.1ze CVE-2026-22796, Low Type confusion PKCS7 digest 3.6-3.0, 1.1.1, 1.0.2, 3.6.1-3.0.19, 1.1.1ze, 1.0.2zn, Low Type confusion Untrusted PKCS#12, PKCS#7, timestamps, or specialized APIs were parsed by these.

According to the advisory, most require customized inputs, restricting remote exploits to particular configurations. OpenSSL 3.6 to 1.0.2 are vulnerable, with the exception of earlier versions lacking features like PBMAC1 or QUIC. Since the impacted code is located outside of boundaries, FIPS modules remain secure.

Vulnerable CVEs in the Fixed Version 3.6 All but 1.0.2-specific 3.6.1 3.5 The majority of 3.5.5 3.4 Most 3.4.4 3.3 A number of 3.3.6 3.0 CMS, BIO, etc. 3.0.19 1.1.1 BIO, OCB, PKCS#12 1.1.1ze (premium) 1.0.2 BIO, PKCS#7 1.0.2zn (premium) Nearly every flaw was discovered by Aisle Research, with Stanislav Fort reporting the most. Others credit Luigino Camastra, Petr Šimeček, Tomas Dulka, and Hamza (Metadust). Fixes by Igor Ustinov, Tomas Mraz, etc.

Steps for Mitigation Upgrade immediately: 3.6.1, 3.5.5, etc. Avoid untrusted PKCS#12/CMS inputs; validate file sizes. For TLS 1.3 compression, set SSL_OP_NO_RX_CERTIFICATE_COMPRESSION.

Due to remote risks, servers that parse timestamps or S/MIME should be patched first. Web servers, VPNs, and cryptocurrency tools are powered globally by OpenSSL. Fast updates stop DoS attacks or worse in production.

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