Vulnerability in Legion of the Bouncy Castle Inc. bc-csharp

[ Description ]Official 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.

[ Fixes ]Fixes and patches

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ Advisories ]Government CERT advisories

• BSI CERT-Bund1 Oct 2026WID-SEC-2026-3713

  Bouncy Castle: Multiple vulnerabilities Translated from German

  Risk mediumCVE-2026-63575CVE-2026-63570CVE-2026-63577+19 more CVEs

[ References ]References

• github.com/bcgit/bc-csharp/commit/eaa42e1e8125b3e2e25e365c4194c7cd5932360b
• github.com/bcgit/bc-csharp/commit/f881400b761134160ec2a05fd27c3e569453788d
• github.com/bcgit/bc-csharp/wiki/CVE-2026-63567