CVE-2026-5477
Severity CVSS v4.0:
HIGH
Type:
CWE-190
Integer Overflow or Wraparound
Publication date:
10/04/2026
Last modified:
27/04/2026
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.
Impact
Base Score 4.0
8.20
Severity 4.0
HIGH
Base Score 3.x
7.50
Severity 3.x
HIGH
Vulnerable products and versions
| CPE | From | Up to |
|---|---|---|
| cpe:2.3:a:wolfssl:wolfssl:*:*:*:*:*:*:*:* | 5.9.0 (including) |
To consult the complete list of CPE names with products and versions, see this page