CVE-2025-13912: 
wolfSSL vulnerability analysis and mitigation

CVE-2025-13912 is a timing side-channel vulnerability in wolfSSL affecting all versions before 5.8.4. Multiple constant-time cryptographic implementations in wolfSSL may be transformed into non-constant-time binary code by LLVM compiler optimizations, resulting in observable timing discrepancies that can lead to information disclosure. The vulnerability was published on December 11, 2025, and affects wolfSSL directly as well as downstream products such as MariaDB packages (cbl2_mariadb_10.6.21-1, azl3_mariadb_10.11.11-1) that bundle vulnerable wolfSSL libraries. It carries a CVSS v4.0 base score of 1.0 (Low) (Feedly, wolfSSL PR).

The root cause is classified as CWE-203 (Observable Discrepancy): wolfSSL's constant-time code paths — designed to prevent timing-based leakage of cryptographic secrets — are inadvertently optimized away by LLVM's compiler backend, producing non-constant-time binary execution. This means that operations intended to take a fixed amount of time regardless of secret values may complete faster or slower depending on the data being processed, creating a measurable timing signal. The fix, merged in pull request #9148, marks the relevant variables as volatile to prevent the compiler from eliminating or reordering the constant-time logic. Exploitation requires local access, high privileges, and passive user interaction, making it a difficult attack to mount in practice (wolfSSL PR, Feedly).

Successful exploitation could allow a local attacker with high privileges to conduct timing side-channel analysis against wolfSSL's cryptographic operations, potentially recovering sensitive cryptographic key material or other secrets protected by the library. The confidentiality impact is limited (low) and there is no direct availability or integrity impact on the vulnerable system itself, though compromise of cryptographic keys could have broader downstream consequences for data confidentiality. Affected deployments include any application using wolfSSL before 5.8.4 compiled with LLVM, as well as MariaDB distributions that bundle the vulnerable library (Feedly).

The primary remediation is to upgrade wolfSSL to version 5.8.4 or later, which includes the fix that marks relevant variables as volatile to prevent LLVM from optimizing away constant-time code paths (wolfSSL PR). For MariaDB deployments, apply vendor-provided security updates that include the patched wolfSSL dependency (e.g., updated cbl2_mariadb and azl3_mariadb packages from Microsoft). As a compensating control where patching is not immediately feasible, restrict local access to systems running vulnerable wolfSSL versions, particularly in environments where cryptographic key material is sensitive. The openembedded/meta-openembedded project has also backported the fix for embedded Linux environments (wolfSSL PR).

The fix was developed by wolfSSL contributor SparkiDev and merged into the wolfSSL master branch on October 1, 2025, ahead of the CVE's public disclosure in December 2025. Red Hat and Microsoft both tracked the vulnerability through their respective advisory systems. The openembedded/meta-openembedded project backported the patch in March 2026, indicating adoption across embedded Linux ecosystems (wolfSSL PR, Microsoft MSRC).