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CVE-2026-63567

7.5, high

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

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
7.5, high high CVSS v3.1
EPSS, next 30 days
0.5% higher than 40.2% of scored CVEs
Exploitation
No public evidence
Published
2 Oct 202626 days ago

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.

Details

Vendor
Legion of the Bouncy Castle Inc.
Product
bc-csharp
Weakness
CWE-203 (opens in a new tab)
Status
Analyzed
Updated
27 Oct 2026
Assigner
91579145-5d7b-4cc5-b925-a0262ff19630

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References 3

Patches and fixes 3

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Legion of the Bouncy Castle Inc. CVEs

Every Legion of the Bouncy Castle Inc. CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-17507 In Bouncy Castle for Java before 1.86, the MLS implementation (org.bouncycastle.mls) holds RFC 9420's uint32 leaf_index in a signed int,… EPSS 0.4% 7.5, high
  • CVE-2026-15999 Improper validation of integrity check value in the AES-CCM implementation (CcmParameters and CcmBlockCipher) in Legion of the Bouncy… EPSS 0.3% 7.5, high
  • CVE-2026-16000 Missing cryptographic step in the DSTU 7624 CCM mode implementation (KCcmBlockCipher) in Legion of the Bouncy Castle Inc EPSS 0.3% 7.5, high
  • CVE-2026-16001 Exposure of the message authentication key through the encryption keystream in the stream mode of IesEngine (an IesEngine constructed… EPSS 0.2% 7.5, high
  • CVE-2026-63566 Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the… EPSS 0.4% 7.5, high
  • CVE-2026-63568 Legion of the Bouncy Castle Inc. bc-csharp Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.3% 7.5, high

Beyond this page

Is CVE-2026-63567 in your network?

This page tells you how dangerous CVE-2026-63567 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

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  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 28 Oct 2026, not the live upstream state.