High

wolfCrypt CMAC integer overflow leading to CMAC/AES-EAX authentication bypass

IdentifiersCVE-2026-5477CWE-190· Integer Overflow or Wraparound

CVE-2026-5477 is a high-severity integer overflow flaw in wolfSSL's wolfCrypt CMAC implementation. In wc_CmacUpdate, the code used the guard if (cmac->totalSz != 0) to skip XOR-chaining on the first block because the initial digest state is all zeros and the XOR is a no-op. The totalSz field is a 32-bit word32; after 2^28 CMAC block flushes, corresponding to 4 GiB of processed data, it wraps to zero. Once this wraparound occurs, the guard incorrectly treats a later block as if it were the first block and discards the live CBC-MAC chaining state. As a result, two messages that share a common suffix beyond the 4 GiB boundary can produce identical CMAC tags, enabling prefix-substitution forgery. The issue also affects AES-EAX constructions that rely on the vulnerable CMAC behavior for authentication of messages larger than 4 GiB.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation breaks message authentication for affected CMAC and AES-EAX uses on inputs larger than 4 GiB. An attacker who has observed one valid message/tag or ciphertext/tag pair for a qualifying message can forge another authenticated message without needing to recover the key or perform cryptanalytic work on the MAC itself. In the AES-EAX case described in the advisory, the attacker can arbitrarily replace the first 4 GiB of ciphertext while preserving tag verification, resulting in authentication bypass and acceptance of attacker-modified data as authentic.

Mitigation

If you can’t patch tonight, do this now.

Until patched, avoid relying on wolfCrypt CMAC or AES-EAX authentication for messages larger than 4 GiB. Enforce application-level size limits below the wraparound threshold, reject or segment oversized messages into independently authenticated chunks, and prefer unaffected authenticated-encryption or MAC constructions where feasible. If AES-EAX is required, ensure implementations are updated before processing attacker-influenced large messages.

Remediation

Patch, then assume compromise.

Update to a fixed wolfSSL release, specifically wolfSSL 5.9.1 or later, which removes the conditional guard and makes the XOR-chaining unconditional in wc_CmacUpdate. The fix preserves correct first-block behavior because the CMAC digest buffer is zero-initialized by wc_InitCmac_ex. Apply vendor patches associated with the wolfSSL 5.9.1 security release.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

WolfsslWolfsslapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

4 SOURCESView more in app

anthropicNews

May 22, 2026

Anthropic's coordinated vulnerability disclosure dashboard

A high-severity integer overflow in wolfSSL involving 32-bit CMAC totalsz wraparound that can enable forgery or prefix substitution.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity3

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-5477

NVD

nvd.nist.gov/vuln/detail/CVE-2026-5477

MITRE CWE · CWE-190

Integer Overflow or Wraparound

Issue Tracking

github.com/wolfSSL/wolfssl/pull/10102

wolfCrypt CMAC integer overflow leading to CMAC/AES-EAX authentication bypass

IdentifiersCVE-2026-5477CWE-190· Integer Overflow or Wraparound