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CVE-2026-63567

7.5 · HIGH

Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc.

Published Oct 2, 2026bouncycastleCWE-203EPSS 0.45%

Overview

CVE-2026-63567 is a high-severity vulnerability affecting bouncycastle bc-csharp. It was published on October 2, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from bouncycastle. Update bc-csharp to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
bouncycastlebc-csharp>= 0, < 2.7.0Affected

References

GitHubgithub.com/bcgit/bc-csharp/commit/eaa42e1e8125b3e2e25e365c4194c7cd5932360bGitHubgithub.com/bcgit/bc-csharp/commit/f881400b761134160ec2a05fd27c3e569453788dGitHubgithub.com/bcgit/bc-csharp/wiki/CVE-2026-63567

How CyberStrike helps

Frequently asked questions

What is CVE-2026-63567?

CVE-2026-63567 is a high-severity vulnerability affecting bouncycastle bc-csharp. It was published on October 2, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-63567?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-63567?

Check the references section for vendor advisories and patches from bouncycastle. Update bc-csharp to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-63567?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-63567 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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