Legion of the Bouncy Castle bc-csharp up to 2.6.x KeyTransRecipientInformation.UnwrapKey random values

CVSS Meta Temp Score
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CTI Interest Score
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3.0$0-$5k0.17

Summaryinfo

A vulnerability categorized as problematic has been discovered in Legion of the Bouncy Castle bc-csharp up to 2.6.x. This affects the function KeyTransRecipientInformation.UnwrapKey. Executing a manipulation can lead to random values. This vulnerability appears as CVE-2026-63573. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Legion of the Bouncy Castle bc-csharp up to 2.6.x. It has been declared as problematic. This vulnerability affects the function KeyTransRecipientInformation.UnwrapKey. The manipulation with an unknown input leads to a random values vulnerability. The CWE definition for the vulnerability is CWE-330. The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-63573 since 07/17/2026. The exploitation appears to be difficult. The attack can be initiated remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1600.001.

Upgrading to version 2.7.0 eliminates this vulnerability.

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Productinfo

Vendor

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 3.1
VulDB Meta Temp Score: 3.0

VulDB Base Score: 3.1
VulDB Temp Score: 3.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Random values
CWE: CWE-330 / CWE-310
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: bc-csharp 2.7.0

Timelineinfo

07/17/2026 CVE reserved
10/02/2026 +77 days Advisory disclosed
10/02/2026 +0 days VulDB entry created
10/02/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-63573 (🔒)
GCVE (CVE): GCVE-0-2026-63573
GCVE (VulDB): GCVE-100-413008

Entryinfo

Created: 10/02/2026 10:16
Changes: 10/02/2026 10:16 (67)
Complete: 🔍
Cache ID: 216::103

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