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CVE-2026-5477— Prefix-substitution forgery via integer overflow in wolfCrypt CMAC

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wolfCrypt CMAC实现中存在整数溢出，可能导致伪造CMAC标签。

AI Predicted 8.1 Difficulty: Hard EPSS 0.35% · P27

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-5477

Vulnerability Information
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Vulnerability Title
Prefix-substitution forgery via integer overflow in wolfCrypt CMAC
Source: CVE Program / CVE List V5
Vulnerability Description
An integer overflow existed in the wolfCrypt CMAC implementation, that could be exploited to forge CMAC tags. The function wc_CmacUpdate used the guard `if (cmac->totalSz != 0)` to skip XOR-chaining on the first block (where digest is all-zeros and the XOR is a no-op). However, totalSz is word32 and wraps to zero after 2^28 block flushes (4 GiB), causing the guard to erroneously discard the live CBC-MAC chain state. Any two messages sharing a common suffix beyond the 4 GiB mark then produce identical CMAC tags, enabling a zero-work prefix-substitution forgery. The fix removes the guard, making the XOR unconditional; the no-op property on the first block is preserved because digest is zero-initialized by wc_InitCmac_ex.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
整数溢出或超界折返
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wolfCrypt CMAC实现中存在整数溢出，可能导致伪造CMAC标签。
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-2026-5477

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III. Intelligence Information for CVE-2026-5477

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Patches & Fixes for CVE-2026-5477 (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-2026-5501 Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf C
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-190

V. Comments for CVE-2026-5477

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