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CVE-2026-5501— Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates

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存在安全漏洞，该漏洞源于OpenSSL兼容层中的wolfSSL_X509_verify_cert函数在攻击者提供由受信任根合法签名但Basic Constraints为CA:FALSE的不可信中间证书时，不会检查叶子证书的签名，可能导致攻击者伪造任意主题名称和公钥的证书。

AI Predicted 9.8 Difficulty: Moderate EPSS 0.22% · P11

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle
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I. Basic Information for CVE-2026-5501

Vulnerability Information
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Vulnerability Title
Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates
Source: CVE Program / CVE List V5
Vulnerability Description
wolfSSL_X509_verify_cert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints `CA:FALSE` that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns `WOLFSSL_SUCCESS` / `X509_V_OK`. The native wolfSSL TLS handshake path (`ProcessPeerCerts`) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
证书验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
wolfSSL 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存在安全漏洞，该漏洞源于OpenSSL兼容层中的wolfSSL_X509_verify_cert函数在攻击者提供由受信任根合法签名但Basic Constraints为CA:FALSE的不可信中间证书时，不会检查叶子证书的签名，可能导致攻击者伪造任意主题名称和公钥的证书。
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-2026-5501

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III. Intelligence Information for CVE-2026-5501

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Patches & Fixes for CVE-2026-5501 (1)

Same Patch Batch · wolfSSL · 2026-04-10 · 6 CVEs total

CVE-2026-5479 wolfSSL EVP ChaCha20-Poly1305 AEAD authentication tag
CVE-2026-5188 Integer underflow in X.509 SAN parsing in wolfSSL
CVE-2026-5466 wc_VerifyEccsiHash missing sanity check
CVE-2026-5477 Prefix-substitution forgery via integer overflow in wolfCrypt CMAC
CVE-2026-5500 Improper Validation of AES-GCM Authentication Tag Length in PKCS#7 Envelope Allows Authent

IV. Related Vulnerabilities

Same product: wolfSSL
Same vendor: wolfSSL
Same weakness: CWE-295

V. Comments for CVE-2026-5501

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