Vulnerability · Published Oct 2, 2026 · Assigned by bcorg
CVE-2026-16000KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used
High 8.7
In plain English
A high-severity security flaw in bc-csharp from Legion of the Bouncy Castle Inc.. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities).
Official description
Missing cryptographic step in the DSTU 7624 CCM mode implementation (KCcmBlockCipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who can observe encrypted messages of known or chosen content to forge ciphertexts with valid authentication tags, via messages encrypted without associated data. The cause is that the G1 block, which binds the nonce, the message length and the parameter flags into the CBC-MAC, was processed only when associated data was present. Without associated data the tag was a CBC-MAC of the plaintext alone, independent of the nonce. Only applications that use KCcmBlockCipher directly and supply no associated data are affected.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Legion of the Bouncy Castle Inc. | bc-csharp | 0 – before 2.7.0 |
Weakness: CWE-325 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N