Wolfssl CVE-2026-5188

CVSS v4.0 score of 2.3 with vectors AV:N/AC:H/AT:P/PR:N/UI:P indicates low severity: network-accessible but requires high complexity, persistent attacker interaction, and user interaction; impact is limited to low confidentiality and availability loss with no integrity impact. The EUVD classification of affected versions up to 5.9.0 suggests this was a tracked vulnerability but EPSS exploitation probability data is unavailable from provided sources. No CISA KEV designation or public proof-of-concept is documented, indicating this is not confirmed actively exploited. Risk is further mitigated by requiring the non-default parsing implementation to be explicitly enabled. Real-world priority should be low unless specific deployments rely on the legacy ASN.1 parser in security-critical certificate validation contexts; the combination of limited impact scope, high attack complexity, required user interaction, and opt-in vulnerable configuration suggests this is a lower-priority issue compared to high-CVSS flaws with simpler attack paths.

An attacker sends a carefully crafted X.509 certificate with a malformed Subject Alternative Name extension containing an entry length larger than its enclosing sequence to a wolfSSL-based application performing certificate validation. If that application has explicitly enabled the original ASN.1 parser (non-default), the parser's length counter underflows during SAN processing, causing subsequent certificate data to be read from incorrect memory offsets. This could disclose adjacent memory contents or trigger a crash depending on memory layout, though exploitation requires the attacker to control the certificate data and relies on high complexity conditions and persistent interaction to achieve a reliable outcome.