Improper Verification of Cryptographic Signature Affecting system.security.cryptography.xml package, versions [8.0.0-preview.1.23110.8, 8.0.4)[9.0.0-preview.1.24080.9, 9.0.18)[10.0.0-preview.1.25080.5, 10.0.10)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published21 Jul 2026
- disclosed20 Jul 2026
- creditLevi Broderick
Introduced: 20 Jul 2026
NewCVE-2026-47304 (opens in a new tab)How to fix?
Upgrade System.Security.Cryptography.Xml to version 8.0.4, 9.0.18, 10.0.10 or higher.
Overview
Affected versions of this package are vulnerable to Improper Verification of Cryptographic Signature in the CheckSignedInfo(KeyedHashAlgorithm) method of SignedXml, which compares only the first SignatureValue.Length bytes of the computed HMAC against the supplied signature value. An attacker can forge a valid HMAC signature and have tampered or attacker-authored signed XML accepted as authentic by supplying a truncated SignatureValue, since only its leading bytes are matched against the full computed HMAC. Exploitation affects applications that verify HMAC-signed XML with SignedXml, and the shorter the truncated HMAC supplied, the smaller the space that must be matched, so a one-byte value reduces the forgery to roughly a 1-in-256 chance.