CVE-2026-103601 HIGH

CVE-2026-103601: CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check

Vendor Legion Of The Bouncy Castle Inc.
Product bc-csharp
Weakness CWE-354
Published October 2, 2026
Last update October 2, 2026

CVSS base score

8.2/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality —
Integrity —

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

What the vulnerability does

01Description

Release of unverified plaintext in the CCM (CcmBlockCipher) and DSTU 7624 CCM (KCcmBlockCipher) AEAD modes in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker to obtain decryptions of ciphertexts of their choosing via forged messages sent to an application that lets the output buffer of a failed decryption be observed, for example through buffer reuse or logging, because decryption wrote the recovered plaintext into the caller-supplied output buffer before checking the authentication tag and left it there when the check failed. Only decryption into a caller-supplied buffer is affected; methods that return a newly allocated array are not.

Key dates

02Disclosure timeline

October 2, 2026 CVE published
October 2, 2026 Record updated