Vulnerability · Published Oct 2, 2026 · Assigned by bcorg
CVE-2026-103601CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check
High 8.2
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 0.3% (higher than 22% of all known vulnerabilities).
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Legion of the Bouncy Castle Inc. | bc-csharp | 0 – before 2.7.0 |
Weakness: CWE-354 · 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