CVE-2026-63573
highObservable discrepancy in the CMS RSA PKCS#1 v1.5 key-transport unwrap (KeyTransRecipientInformation.UnwrapKey) in Legion of the Bouncy Castle Inc.
Vendor / product: Bouncycastle — bc-csharp
Observable discrepancy in the CMS RSA PKCS#1 v1.5 key-transport unwrap (KeyTransRecipientInformation.UnwrapKey) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who holds a captured CMS EnvelopedData message, and who can submit many modified messages to an application that decrypts them with the recipient's RSA private key and reveals how decryption failed, to recover the captured message's content-encryption key and so its content, via a Bleichenbacher-style adaptive chosen-ciphertext attack, because a key-transport ciphertext with invalid PKCS#1 v1.5 padding is rejected during unwrap with a distinct "bad padding in message." CmsException instead of being replaced by a random key, so it can be told apart from a correctly padded ciphertext, which fails only later at content decryption.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Affected products
Weakness classification (CWE)
Source: NVD / CISA. “NVD-CWE-Other” and “NVD-CWE-noinfo” mean NVD could not assign a specific weakness.
Mitigation & advisories
References
- https://github.com/bcgit/bc-csharp/commit/85679cc7023adf4e2a0650b88a1f4f98679c7463 91579145-5d7b-4cc5-b925-a0262ff19630
- https://github.com/bcgit/bc-csharp/commit/c38b4790e2aef68f116a551f73b94ea05cb5590c 91579145-5d7b-4cc5-b925-a0262ff19630
- https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63573 91579145-5d7b-4cc5-b925-a0262ff19630