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CVE-2026-6331— HMAC zero-length tag forgery in EVP_DigestVerifyFinal

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是wolfSSL公司开源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 3.15.5版本至5.9.1及之前版本存在加密问题漏洞，该漏洞源于EVP_DigestVerifyFinal中HMAC零长度标签伪造，在OpenSSL兼容的HMAC验证路径中，提供的签名长度仅检查不超过MAC长度，导致零长度或被截断的标签可通过验证。

AI Predicted 5.9 Difficulty: Moderate EPSS 0.19% · P8

Affected Version Matrix 1

VendorProduct Version RangeStatus
wolfSSL wolfSSL 3.15.5≤ 5.9.1 affected
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I. Basic Information for CVE-2026-6331

Vulnerability Information
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Vulnerability Title
HMAC zero-length tag forgery in EVP_DigestVerifyFinal
Source: CVE Program / CVE List V5
Vulnerability Description
HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
wolfSSL 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
wolfSSL是wolfSSL公司开源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 3.15.5版本至5.9.1及之前版本存在加密问题漏洞，该漏洞源于EVP_DigestVerifyFinal中HMAC零长度标签伪造，在OpenSSL兼容的HMAC验证路径中，提供的签名长度仅检查不超过MAC长度，导致零长度或被截断的标签可通过验证。
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 3.15.5 ~ 5.9.1 -

II. Public POCs for CVE-2026-6331

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III. Intelligence Information for CVE-2026-6331

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Patches & Fixes for CVE-2026-6331 (1)

Vendor Pages for CVE-2026-6331 (1)

Same Patch Batch · wolfSSL · 2026-06-25 · 32 CVEs total

CVE-2026-6329 PKCS#12 MAC verification uses attacker-controlled comparison length
CVE-2026-55958 Renesas TSIP TLS 1.3 transcript buffer out-of-bounds write in tsip_StoreMessage
CVE-2026-55960 Un-negotiated Raw Public Key (RFC 7250) accepted in place of X.509, bypassing chain valida
CVE-2026-55967 AES-GCM streaming APIs do not reject >64 GiB cumulative single messages, enabling counter
CVE-2026-55961 wolfSSL_PKCS7_verify() reports success for degenerate (certs-only) PKCS#7 with no signer
CVE-2026-55962 TLS 1.3 post-handshake authentication: server accepts Finished without client Certificate/
CVE-2026-55964 Chain intermediate CA:TRUE without keyCertSign accepted as a signing CA (temporary CA exem
CVE-2026-8720 HMAC-BLAKE2 final discards message when key length exceeds block size
CVE-2026-12340 Out-of-bounds heap read in SM2/SM3 certificate Subject Key Identifier computation
CVE-2026-10512 X25519 x86_64 assembly final reduction leaves non-canonical field element
CVE-2026-10097 ML-KEM-1024 x64 AVX2 incomplete cipher text comparison enables IND-CCA2 break and static p
CVE-2026-10098 OCSP CertID serial-number length-confusion in wolfSSL_OCSP_resp_find_status
CVE-2026-10592 Wildcard DNS SAN bypasses CA name-constraint checks
CVE-2026-11310 X.509 trust-chain bypass in wolfSSL_X509_verify_cert() via untrusted intermediate anchorin
CVE-2026-11703 Missing SNI/ALPN binding on stateful (session-ID) TLS session resumption
CVE-2026-11999 X.509 trust-chain bypass via path-depth exhaustion in wolfSSL_X509_verify_cert()
CVE-2026-7532 iPAddress name constraints not enforced when WOLFSSL_IP_ALT_NAME is undefined
CVE-2026-6679 DTLS 1.3 ACK serialization heap buffer overflow via integer truncation
CVE-2026-6094 Heap buffer overread in wc_PKCS7_DecodeEnvelopedData parsing crafted PKCS7 EnvelopedData
CVE-2026-6731 X.509 name constraint bypass via Subject CN treated as a DNS name

Showing top 20 of 32 CVEs. View all on vendor page → →

IV. Related Vulnerabilities

Same product: wolfSSL
Same vendor: wolfSSL
Same weakness: CWE-347

V. Comments for CVE-2026-6331

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