CVE-2026-5477 (GCVE-0-2026-5477)

Vulnerability from cvelistv5 – Published: 2026-04-10 05:06 – Updated: 2026-04-10 14:04
VLAI?
Title
Prefix-substitution forgery via integer overflow in wolfCrypt CMAC
Summary
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.
Severity ?
8.2 (High)
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
CWE
  • CWE-190 - Integer overflow or wraparound
Assigner
References
Impacted products
Vendor Product Version
wolfSSL wolfSSL Affected: 0 , ≤ 5.9.0 (semver)
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Credits
Calif.io in collaboration with Claude and Anthropic Research
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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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