CVE-2026-5448: wolfSSL X.509 Buffer Overflow Vulnerability

CVE-2026-5448 Overview

A heap-based buffer overflow vulnerability has been identified in wolfSSL's X.509 certificate parsing functionality. The vulnerability exists in the wolfSSL_X509_notAfter and wolfSSL_X509_notBefore functions within the compatibility layer API. When processing date fields from a specially crafted X.509 certificate, a buffer overflow condition can occur, potentially leading to denial of service.

Critical Impact

Applications directly calling the affected X.509 date parsing APIs may be vulnerable to denial of service through crafted certificates. Standard TLS operations and certificate verification are not affected.

Affected Products

• wolfSSL library (versions using the compatibility layer API)
• Applications directly calling wolfSSL_X509_notAfter function
• Applications directly calling wolfSSL_X509_notBefore function

Discovery Timeline

• 2026-04-10 - CVE CVE-2026-5448 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-5448

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow). The issue occurs within wolfSSL's OpenSSL compatibility layer when applications directly invoke the wolfSSL_X509_notAfter or wolfSSL_X509_notBefore functions to extract certificate validity dates.

When parsing date fields from a maliciously crafted X.509 certificate, the functions fail to properly validate the size of input data before copying it to a fixed-size buffer. This can result in a heap-based buffer overflow condition. Notably, this vulnerability has a limited attack surface as it requires adjacent network access and specific application conditions to trigger.

The vulnerability does not affect standard TLS handshake operations or the internal certificate verification mechanisms within wolfSSL. Only applications that explicitly call these two compatibility layer APIs to parse certificate dates are at risk.

Root Cause

The root cause is insufficient bounds checking when parsing date fields from X.509 certificates through the compatibility layer. The wolfSSL_X509_notAfter and wolfSSL_X509_notBefore functions do not adequately validate the length of date field data before processing, allowing oversized or malformed date values to overflow the destination buffer on the heap.

Attack Vector

The attack vector requires adjacent network access. An attacker would need to supply a crafted X.509 certificate containing malformed date fields to an application that directly calls the vulnerable API functions. The attack conditions include:

• Target application must explicitly call wolfSSL_X509_notAfter or wolfSSL_X509_notBefore
• Attacker must be able to supply a malicious certificate to the application
• Standard TLS connections and certificate verification paths are not vulnerable

The practical exploitability is limited due to these specific requirements, and the impact is constrained to potential denial of service through memory corruption affecting availability.

Detection Methods for CVE-2026-5448

Indicators of Compromise

• Unexpected application crashes when processing X.509 certificates
• Memory corruption errors in applications using wolfSSL compatibility layer
• Abnormal heap memory usage patterns during certificate parsing operations

Detection Strategies

• Monitor for crashes or exceptions in wolfSSL-based applications during certificate processing
• Implement application-level logging for calls to wolfSSL_X509_notAfter and wolfSSL_X509_notBefore
• Use memory debugging tools (e.g., AddressSanitizer, Valgrind) during testing to detect buffer overflow conditions
• Review application code for direct usage of the affected compatibility layer functions

Monitoring Recommendations

• Enable heap corruption detection in production environments where feasible
• Monitor application stability metrics for wolfSSL-dependent services
• Set up alerts for repeated crashes in certificate processing code paths

How to Mitigate CVE-2026-5448

Immediate Actions Required

• Review application code to identify direct usage of wolfSSL_X509_notAfter and wolfSSL_X509_notBefore functions
• Update wolfSSL to a patched version that addresses this buffer overflow
• Validate all X.509 certificates from untrusted sources before processing date fields
• Consider implementing additional input validation for certificate data in affected applications

Patch Information

A fix has been developed and is available through the wolfSSL GitHub Pull Request #10071. Organizations using wolfSSL should apply this patch or update to a version that includes this fix.

The patch addresses the buffer overflow by implementing proper bounds checking in the date field parsing logic within the compatibility layer API functions.

Workarounds

• Avoid direct calls to wolfSSL_X509_notAfter and wolfSSL_X509_notBefore until patch is applied
• Implement certificate validation and sanitization before passing to affected functions
• Use alternative methods to extract certificate date information if available in your application architecture
• Restrict certificate sources to trusted origins only to reduce attack surface