CVE-2026-5477

OVERVIEW CVE-2026-5477 is an integer overflow vulnerability in the wolfSSL wolfCrypt library's CMAC (Cipher-based Message Authentication Code) implementation. The flaw exists in the wc_CmacUpdate function, where a 32-bit counter wraps to zero after processing 4 GiB of data, causing the function to incorrectly skip XOR-chaining operations on subsequent blocks. This allows an attacker to forge valid CMAC tags for messages sharing common suffixes beyond the 4 GiB threshold, effectively breaking the authentication mechanism. SEVERITY The vulnerability has a FAUCET Risk Score of 49.0 out of 100, indicating moderate severity. The attack requires no special conditions beyond processing sufficient data to trigger the integer wrap, making the attack complexity low. The impact is cryptographically significant: an attacker can perform zero-effort prefix-substitution forgeries, replacing the beginning of an authenticated message while maintaining a valid tag. However, the practical exploitation window is limited by the 4 GiB data processing requirement, which constrains real-world applicability in many scenarios. EXPLOITATION STATUS There is currently no indication of active exploitation in the wild. The vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog, and community attention remains minimal as reflected by the low EPSS score of 0.00055. No public exploit code is reported to be available. Organizations using wolfSSL should prioritize patching based on their specific use cases, particularly systems handling high-volume data streams where the 4 GiB threshold could realistically be reached.