Critical OpenSSL Vulnerabilities Expose Systems to Remote Code Execution
On January 27, 2026, the OpenSSL Project released patches addressing 12 security vulnerabilities, including a high-severity flaw that could enable remote code execution (RCE). These vulnerabilities primarily affect applications that process untrusted data, such as S/MIME emails, and underscore the importance of timely software updates to maintain system security.
High-Severity Vulnerability: CVE-2025-15467
The most critical of these vulnerabilities, identified as CVE-2025-15467, involves a stack overflow in the parsing of CMS (Cryptographic Message Syntax) AuthEnvelopedData when using AEAD (Authenticated Encryption with Associated Data) ciphers like AES-GCM. An attacker can craft a CMS message with an oversized Initialization Vector (IV) in the ASN.1 parameters, leading to a stack overflow before authentication checks are performed. This flaw can result in application crashes or potentially allow remote code execution in applications that handle untrusted CMS or PKCS#7 data, such as those processing S/MIME emails.
The risk is particularly high for applications that parse remote CMS content, as no key is required to trigger the overflow. The exploitability of this vulnerability depends on platform-specific defenses like Address Space Layout Randomization (ASLR), but the presence of a stack write primitive makes it a severe threat. OpenSSL has rated this vulnerability as High severity.
Moderate-Severity Vulnerability: CVE-2025-11187
Another notable vulnerability, CVE-2025-11187, pertains to improper validation in the PBMAC1 function within PKCS#12 files. This flaw can lead to stack overflows or null pointer dereferences in OpenSSL versions 3.6 through 3.4. Maliciously crafted PKCS#12 files can trigger buffer overflows during key derivation if the key length exceeds 64 bytes.
Low-Severity Vulnerabilities
Several low-severity issues were also addressed, including:
– CVE-2025-69419: Out-of-bounds write in PKCS#12 friendlyName processing.
– CVE-2025-69421: Null pointer dereference in PKCS#12 decryption.
– CVE-2026-22795: Type confusion in PKCS#12 handling.
These vulnerabilities primarily affect the parsing of untrusted PKCS#12, PKCS#7, and timestamp data, as well as certain APIs. Exploitation typically requires crafted inputs, limiting the potential for remote attacks to specific scenarios.
Affected Versions and Patches
The vulnerabilities impact OpenSSL versions from 3.6 down to 1.0.2, excluding older branches that lack features like PBMAC1 or QUIC. The FIPS modules remain unaffected, as the vulnerable code resides outside their boundaries.
The following table summarizes the affected versions and their corresponding patched versions:
| Version | Vulnerable CVEs | Fixed Version |
|———|—————–|—————|
| 3.6 | All except 1.0.2-specific | 3.6.1 |
| 3.5 | Most | 3.5.5 |
| 3.4 | Most | 3.4.4 |
| 3.3 | Several | 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) |
Mitigation Steps
To protect systems from these vulnerabilities, it is crucial to:
1. Upgrade OpenSSL: Immediately update to the latest patched versions: 3.6.1, 3.5.5, 3.4.4, 3.3.6, 3.0.19, 1.1.1ze, or 1.0.2zn, as applicable.
2. Avoid Untrusted Inputs: Refrain from processing untrusted PKCS#12 or CMS data.
3. Validate File Sizes: Implement checks to ensure that file sizes are within expected parameters.
4. Configure TLS Settings: For TLS 1.3 certificate compression, set `SSL_OP_NO_RX_CERTIFICATE_COMPRESSION` to mitigate related risks.
Servers that parse S/MIME emails or timestamps should prioritize patching due to the higher risk of remote exploitation.
Conclusion
OpenSSL is integral to the security infrastructure of numerous web servers, VPNs, and cryptographic tools worldwide. Promptly applying these updates is essential to prevent potential denial-of-service attacks or more severe exploits in production environments. Administrators should also review dependencies managed through package managers to ensure all components are up to date.
