| tiêu đề | GitHub Dropbear 2025.89 Improper Verification of Cryptographic Signature |
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| Mô tả | The specific issue is located in curve25519.c:
Line 484 directly uses s+32 for computation, with no validation for S >= L at any point.
According to the RFC 8032 §5.1.7 specification, an out-of-bounds S should be rejected. Without this check, we can generate an equivalent signature by constructing S' = S + L. My local testing confirms that Dropbear's verification process accepts both the original signature and its S+L variant. Furthermore, the paper "The Provable Security of Ed25519: Theory and Practice" by Jacqueline Brendel, Cas Cremers, Dennis Jackson, and Mang Zhao (https://ieeexplore.ieee.org/stampPDF/getPDF.jsp?arnumber=9519456) emphasizes that strictly rejecting such non-canonical signatures is necessary to maintain Strong Existential Unforgeability under Chosen Message Attacks (SUF-CMA).
Historically, there have been multiple signature malleability vulnerabilities in other projects (e.g., CVE-2020-36843, CVE-2024-45193). This inconsistency with the specification breaks signature uniqueness and could potentially impact higher-level security policies or auditing logic that rely on it. |
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| Nguồn | ⚠️ https://github.com/mkj/dropbear/issues/406 |
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| Người dùng | pythok (UID 95793) |
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| Đệ trình | 23/02/2026 17:02 (cách đây 7 các tháng) |
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| Kiểm duyệt | 07/03/2026 10:07 (12 days later) |
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| Trạng thái | được chấp nhận |
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| Mục VulDB | 349652 [mkj Dropbear đến 2025.89 S Range Check src/curve25519.c unpackneg xác thực yếu] |
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| điểm | 20 |
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