CVE-2026-5448: 
wolfSSL vulnerability analysis and mitigation

CVE-2026-5448 is a heap-based buffer overflow vulnerability in wolfSSL affecting the wolfSSL_X509_notAfter and wolfSSL_X509_notBefore compatibility layer API functions. A buffer overflow may occur when parsing date fields from a crafted X.509 certificate when these two APIs are called directly by an application; standard TLS and certificate verification operations in wolfSSL are not affected. All wolfSSL versions prior to 5.9.1 are affected. The vulnerability was published on April 10, 2026, with the fix merged on April 2, 2026. It carries a CVSS v3.1 base score of 4.3 (Medium) and a CVSS v4.0 base score of 2.3 (Low) (GitHub Advisory, wolfSSL PR).

The root cause is a heap-based buffer overflow (CWE-122) in the wolfSSL_X509_notAfter and wolfSSL_X509_notBefore functions within wolfSSL's OpenSSL compatibility layer. The overflow originates in CopyDecodedToX509() where the date length is capped at MAX_DATE_SZ (32 bytes), but the copy-at-offset-2 pattern in the getter functions requires a safe maximum of CTC_DATE_SIZE - 2 (30 bytes), allowing a 2-byte overflow into adjacent heap memory. Exploitation requires an attacker with adjacent network access to supply a crafted X.509 certificate to an application that directly calls these two API functions; applications using only standard TLS operations are not vulnerable. The fix introduced a CopyDateToASN1_TIME() helper that consolidates copy logic and enforces proper bounds, along with corrected setter validation to align with getter limits (wolfSSL PR, GitHub Advisory).

Successful exploitation can cause a denial of service (DoS) condition in applications that directly invoke the affected wolfSSL compatibility API functions when processing attacker-supplied X.509 certificates. There is no impact to confidentiality or integrity — the vulnerability is limited to availability, with a low availability impact on the vulnerable system only. The narrow attack surface (adjacent network access required, specific API usage required) significantly limits the practical scope of exploitation (GitHub Advisory, wolfSSL PR).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of publication (GitHub Advisory). The EPSS score is approximately 0.015–0.019%, placing it in the 5th percentile for exploitation likelihood within 30 days. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires adjacent network positioning and a target application that directly calls the affected APIs, further reducing practical exploitability.

Upgrade wolfSSL to version 5.9.1 or later, which includes the fix merged on April 2, 2026 (PR #10071). Applications that do not directly call wolfSSL_X509_notAfter or wolfSSL_X509_notBefore are not affected and do not require immediate action. Developers should audit their codebase for direct use of these two compatibility layer APIs and prioritize patching those components (wolfSSL PR, GitHub Advisory).

The vulnerability was discussed on the oss-security mailing list shortly after disclosure. Community review during the pull request process (notably by contributor programsurf) identified that the initial patch addressed only the getter bounds check and not the root cause in CopyDecodedToX509() or setter validation, prompting an expanded fix before merge. The wolfSSL team responded promptly, incorporating most of the community feedback into the final patch (oss-sec, wolfSSL PR).