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CVE-2026-5503— out-of-bounds write in TLSX_EchChangeSNI via attacker-controlled publicName

Quick assessment

Affected
wolfSSL wolfSSL
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

wolfSSL（CyaSSL）是美国wolfSSL公司的一个针对嵌入式系统开发人员使用的小的、可移植的嵌入式SSL编程库。 wolfSSL（CyaSSL）存在安全漏洞，该漏洞源于TLSX_EchChangeSNI函数无条件设置扩展，可能导致将攻击者控制的publicName附加到共享的WOLFSSL_CTX并触发越界写入。

AI Predicted 9.8 Difficulty: Moderate EPSS 0.45% · P37

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-5503

Vulnerability Information
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Vulnerability Title
out-of-bounds write in TLSX_EchChangeSNI via attacker-controlled publicName
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
wolfSSL（CyaSSL） 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
wolfSSL（CyaSSL）是美国wolfSSL公司的一个针对嵌入式系统开发人员使用的小的、可移植的嵌入式SSL编程库。 wolfSSL（CyaSSL）存在安全漏洞，该漏洞源于TLSX_EchChangeSNI函数无条件设置扩展，可能导致将攻击者控制的publicName附加到共享的WOLFSSL_CTX并触发越界写入。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
wolfSSL wolfSSL 0 ~ 5.9.0 -

II. Public POCs for CVE-2026-5503

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III. Intelligence Information for CVE-2026-5503

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Patches & Fixes for CVE-2026-5503 (1)

Same Patch Batch · wolfSSL · 2026-04-09 · 16 CVEs total

CVE-2026-5263 URI nameConstraints not enforced in ConfirmNameConstraints()
CVE-2026-5187 Heap Out-of-Bounds Write in DecodeObjectId() in wolfSSL
CVE-2026-5264 DTLS 1.3 ACK heap buffer overflow
CVE-2026-5295 Stack Buffer Overflow in wolfSSL PKCS7 wc_PKCS7_DecryptOri() via Oversized OID
CVE-2026-5393 OOB Read in DoTls13CertificateVerify with WOLFSSL_DUAL_ALG_CERTS
CVE-2026-5446 wolfSSL ARIA-GCM TLS 1.2/DTLS 1.2 GCM nonce reuse
CVE-2026-5504 PKCS7 CBC Padding Oracle — Plaintext Recovery
CVE-2026-5447 Heap buffer overflow in CertFromX509() via AuthorityKeyIdentifier
CVE-2026-5778 Integer underflow leads to out-of-bounds access in sniffer ChaCha decrypt path.
CVE-2026-5772 MatchDomainName 1-Byte Stack Buffer Over-Read in Hostname Validation
CVE-2026-5507 Session Cache Restore — Arbitrary Free via Deserialized Pointer
CVE-2026-5194 wolfSSL ECDSA Certificate Verification
CVE-2026-5392 wolfSSL heap OOB read in PKCS7 SignedData streaming
CVE-2026-5460 Heap Use-After-Free in PQC Hybrid KeyShare Error Cleanup in wolfSSL TLS 1.3
CVE-2026-5448 1-2 Byte Buffer Overflow in wolfSSL_X509_notAfter/notBefore

IV. Related Vulnerabilities

Same product: wolfSSL
Same vendor: wolfSSL
Same weakness: CWE-787

V. Comments for CVE-2026-5503

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