CVE-2026-63573
highpriority · track · 0EPSS 0.003 · 23 %ileDEEPSS · scored 2026-10-27
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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 4.6–8.2
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (12)
Products and version ranges known to be affected.
advisories (1)
Vendor and ecosystem advisories describing this.
- WID-SEC-W-2026-3713Bouncy Castle: Mehrere SchwachstellenDeutsch2026-10-01csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Bouncy Castle ausnutzen, um Sicherheitsvorkehrungen zu umgehen, Daten zu manipulieren oder offenzulegen und einen Denial-of-Service-Zustand auszulösen.
sources
Which sources assert this record, and when.
references (3) nvd
External citations — patches, advisories, analysis.
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