by Kastro
Paper/Archive/CVE-2026-5503

CVE-2026-5503

wolfSSL wolfSSL — out-of-bounds write in TLSX_EchChangeSNI via attacker-controlled publicName

EPSS 0.5%CVSS 9.1
critical.is priorityof 100
36
CVSS 9.1 (NVD)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 43.5.435 × 208.7No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
wolfSSL≤ 5.9.0–CNA

Scores by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
wolfSSL (CNA)6.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: partial

References

refgithub.com/wolfSSL/wolfssl/pull/10102