Authentication bypass via CMAC counter wrap
Published Apr 10, 2026 · Updated Apr 10, 2026
Integer overflow in wolfCrypt CMAC in wolfSSL 5.9.0 and earlier allows remote attackers to forge authentication tags for messages over 4 GiB. In wc_CmacUpdate, the 32-bit totalSz counter wraps to zero after 2^28 block flushes, causing a first-block guard to discard the live CBC-MAC chain. Exploitation requires one valid ciphertext and tag for a message over 4 GiB; the attacker can then replace its first 4 GiB while preserving a valid tag.
Summary
What happened
Integer overflow in wolfCrypt CMAC in wolfSSL 5.9.0 and earlier allows remote attackers to forge authentication tags for messages over 4 GiB. In wc_CmacUpdate, the 32-bit totalSz counter wraps to zero after 2^28 block flushes, causing a first-block guard to discard the live CBC-MAC chain. Exploitation requires one valid ciphertext and tag for a message over 4 GiB; the attacker can then replace its first 4 GiB while preserving a valid tag.
The record
- CVE
- CVE-2026-5477
- Published
- Apr 10, 2026
- Updated
- Apr 10, 2026
- Vendor
- wolfSSL
- Product
- wolfSSL
- Classifications
- CWE-190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 10, 2026CVE publishedPublication date reported by the CVE source.
- Apr 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <=5.9.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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