CVE-2026-5477
An integer overflow existed in the wolfCrypt CMAC implementation, that could be exploited to forge CMAC tags.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.42%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 4.0
- 8.2 HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.42% probability · 35th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-190
- Affected
- wolfssl/wolfssl
- Source
- facts@wolfssl.com
References
- https://github.com/wolfSSL/wolfssl/pull/10102Issue Tracking
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.