HMAC reconstruction via variable-time signature comparison
Published Jun 2, 2025 · Updated Jun 2, 2025
Observable timing discrepancy in SignXML's HMAC verifier before 4.0.4 allows remote attackers to infer correct HMAC values. In signxml/verifier.py, XMLVerifier.verify() finalizes the computed HMAC and compares raw_signature with Python equality rather than a constant-time verification operation, leaking match information through execution time. Exposure requires X.509 validation to be disabled, an hmac_key to be configured, and repeated attacker-controlled signature checks; the published impact is limited to HMAC information disclosure.
Summary
What happened
Observable timing discrepancy in SignXML's HMAC verifier before 4.0.4 allows remote attackers to infer correct HMAC values. In signxml/verifier.py, XMLVerifier.verify() finalizes the computed HMAC and compares raw_signature with Python equality rather than a constant-time verification operation, leaking match information through execution time. Exposure requires X.509 validation to be disabled, an hmac_key to be configured, and repeated attacker-controlled signature checks; the published impact is limited to HMAC information disclosure.
The record
- CVE
- CVE-2025-48995
- Published
- Jun 2, 2025
- Updated
- Jun 2, 2025
- Vendor
- XML-Security
- Product
- SignXML
- Classifications
- CWE-208
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 2, 2025CVE publishedPublication date reported by the CVE source.
- Jun 2, 2025Record 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=< 4.0.4
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
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Your stack
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