CVE-2026-5447: X.509 Certificate Buffer Overflow Flaw

CVE-2026-5447 Overview

A heap buffer overflow vulnerability exists in the wolfSSL library's CertFromX509 function due to incorrect size handling of the AuthorityKeyIdentifier extension during X.509 certificate conversion. This memory corruption flaw can be triggered when processing maliciously crafted certificates, potentially allowing attackers to corrupt heap memory and affect application integrity.

Critical Impact

Heap buffer overflow during X.509 certificate processing could allow remote attackers to corrupt memory and potentially compromise system integrity through malformed AuthorityKeyIdentifier extensions.

Affected Products

• wolfSSL library (versions prior to the fix in pull request #10112)

Discovery Timeline

• April 9, 2026 - CVE-2026-5447 published to NVD
• April 9, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5447

Vulnerability Analysis

This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow) and occurs within the CertFromX509 function of the wolfSSL cryptographic library. The flaw is triggered during the internal conversion of X.509 certificates when the AuthorityKeyIdentifier (AKI) extension is processed.

The AuthorityKeyIdentifier extension is a critical component in X.509 certificate chains, used to identify the public key corresponding to the private key used to sign a certificate. When wolfSSL parses this extension, a size confusion error causes the library to miscalculate the buffer requirements for storing the AKI data, resulting in a heap buffer overflow condition.

This vulnerability can be exploited remotely over the network, though successful exploitation requires specific conditions to be met. The attack does not require authentication or user interaction, making it a potential concern for TLS/SSL implementations using affected wolfSSL versions.

Root Cause

The root cause stems from improper size handling when processing the AuthorityKeyIdentifier extension during X.509 certificate conversion. The CertFromX509 function fails to correctly calculate or validate the size of the AKI extension data before copying it into a heap-allocated buffer. This size confusion leads to writing beyond the allocated buffer boundaries, corrupting adjacent heap memory.

Attack Vector

An attacker can exploit this vulnerability by crafting a malicious X.509 certificate containing a specially constructed AuthorityKeyIdentifier extension with unexpected size parameters. When a vulnerable wolfSSL implementation processes this certificate (such as during TLS handshake or certificate validation), the heap buffer overflow is triggered.

The attack can be delivered through any network protocol that processes X.509 certificates, including:

• TLS/SSL connections where the server or client presents malformed certificates
• Certificate chain validation operations
• Any application-level certificate parsing using wolfSSL

The vulnerability exploits the size mismatch between the expected and actual AuthorityKeyIdentifier extension data. When the internal conversion routine allocates a buffer based on an incorrect size calculation and subsequently writes the actual extension data, the overflow occurs. This can corrupt heap metadata, adjacent heap objects, or other critical memory structures depending on the heap layout.

Detection Methods for CVE-2026-5447

Indicators of Compromise

• Unexpected application crashes or segmentation faults during TLS handshake operations
• Heap corruption errors or memory-related exceptions when processing certificates
• Abnormal certificate validation failures accompanied by memory errors
• Core dumps indicating heap overflow in wolfSSL library functions

Detection Strategies

• Monitor for abnormal crashes in applications using wolfSSL during certificate processing
• Implement heap canary or guard page protections to detect overflow attempts
• Use Address Sanitizer (ASan) in development/testing environments to catch buffer overflows
• Deploy intrusion detection rules to identify malformed X.509 certificates with unusual AuthorityKeyIdentifier extensions

Monitoring Recommendations

• Enable verbose logging for certificate processing operations in wolfSSL-based applications
• Monitor application crash reports for patterns indicating heap corruption
• Implement certificate validation logging to capture details of malformed certificates
• Track memory allocation patterns in wolfSSL certificate processing functions

How to Mitigate CVE-2026-5447

Immediate Actions Required

• Update wolfSSL to a version that includes the fix from GitHub Pull Request #10112
• Review and audit any applications using wolfSSL for certificate processing
• Consider implementing additional certificate validation at the application layer
• Enable heap protection mechanisms (ASLR, heap canaries) where available

Patch Information

The vulnerability has been addressed in the wolfSSL project through Pull Request #10112. Organizations using wolfSSL should review this pull request and update to a patched version that includes this fix. The patch corrects the size handling logic in the CertFromX509 function to properly calculate buffer requirements for the AuthorityKeyIdentifier extension.

Workarounds

• If immediate patching is not possible, consider implementing strict certificate validation at network boundaries
• Use Web Application Firewalls (WAF) or TLS inspection proxies that can filter malformed certificates before they reach vulnerable applications
• Compile applications with stack and heap protection mechanisms enabled
• Consider using runtime memory protection tools to detect and prevent heap overflow exploitation

The recommended mitigation approach involves reviewing and applying the fix from the wolfSSL repository. Administrators should consult the GitHub Pull Request for wolfSSL for technical details on the patch implementation.