CVE-2026-5503: wolfSSL

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

In TLSX_EchChangeSNI, the ctx->extensions branch set extensions unconditionally even when TLSX_Find returned NULL. This caused TLSX_UseSNI to attach the attacker-controlled publicName to the shared WOLFSSL_CTX when no inner SNI was configured. TLSX_EchRestoreSNI then failed to clean it up because its removal was gated on serverNameX != NULL. The inner ClientHello was sized before the pollution but written after it, causing TLSX_SNI_Write to memcpy 255 bytes past the allocation boundary.

Affected products

• wolfSSL wolfSSL: up to and including 5.9.0

Published 2026-04-09. Last modified 2026-06-17.