Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not.
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Affected Vendors & Products
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History
Tue, 27 Oct 2026 16:30:00 +0000
| Type | Values Removed | Values Added |
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| First Time appeared |
Bouncycastle
Bouncycastle bc-csharp |
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| CPEs | cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Bouncycastle
Bouncycastle bc-csharp |
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| Metrics |
cvssV3_1
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Sun, 04 Oct 2026 22:15:00 +0000
| Type | Values Removed | Values Added |
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| First Time appeared |
Legion Of The Bouncy Castle Inc.
Legion Of The Bouncy Castle Inc. bc-csharp |
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| Vendors & Products |
Legion Of The Bouncy Castle Inc.
Legion Of The Bouncy Castle Inc. bc-csharp |
Sun, 04 Oct 2026 06:30:00 +0000
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ssvc
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Fri, 02 Oct 2026 07:15:00 +0000
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| Description | Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not. | |
| Title | IesEngine block-cipher mode checks padding before MAC (CBC padding oracle) | |
| Weaknesses | CWE-203 | |
| References |
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| Metrics |
cvssV4_0
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Status: PUBLISHED
Assigner: bcorg
Published: 2026-10-02T06:58:32.487Z
Updated: 2026-10-02T18:09:54.933Z
Reserved: 2026-07-16T23:48:46.076Z
Link: CVE-2026-63567
Updated: 2026-10-02T18:09:48.244Z
Status : Analyzed
Published: 2026-10-02T07:16:37.127
Modified: 2026-10-27T16:20:42.560
Link: CVE-2026-63567
No data.