EUVD-2026-21234
GHSA-65xm-pfx9-g5p3
CVSS Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3Description
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.
Analysis
Buffer overflow in WolfSSL's TLSX_SNI_Write function allows remote unauthenticated attackers to corrupt memory by sending a specially crafted TLS ClientHello with ECH (Encrypted Client Hello) and SNI extension data. The vulnerability occurs when TLSX_EchChangeSNI unconditionally sets extensions even when no inner SNI is configured, causing attacker-controlled SNI data to be written 255 bytes beyond the allocated buffer boundary during ClientHello serialization. …
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