CVE-2026-71883: Native AES packet cipher returns the raw AES key on an alias
In Bouncy Castle for Java LTS before 2.73.13, the one-shot native packet ciphers for AES-CBC, CCM, CFB, CTR, GCM and GCM-SIV released the caller's key, IV and additional authenticated data arrays with JNI's ReleaseByteArrayElements in mode 0, which commits the native copy back into the Java array. Those arrays are read-only to the native code, and on a JVM that returns a copy rather than a pin the copy still holds the input bytes as they were read. The output buffer is taken through a separate critical region and committed first, so where an application passed the same Java array as both an input and the destination - encrypting in place over KeyParameter.getKey(), for example - the later mode-0 release of the key wrote the unchanged key bytes over the ciphertext that had just been produced. The call still returned the correct output length, so an application encrypting in place over its own key array was handed the raw AES key where it expected ciphertext, with nothing in the API to indicate it, and would transmit or store the key in place of the message. The read-only input arrays are now released with JNIABORT, freeing the native copy without copying it back, and mode 0 is reserved for arrays the native code wrote. The pure-Java packet ciphers and the streaming native modes are not affected. Bouncy Castle for Java (bcprov) is not affected, as it ships no native implementations.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Bouncy Castle for Java LTSto a version that resolves this vulnerability.Fixed in 2.73.13
Event History
Frequently Asked Questions
Which applications are exposed to key disclosure?
Exposure requires use of a one-shot native AES packet cipher in an affected Bouncy Castle for Java LTS release, with the same Java array supplied as both a read-only input and the output destination. An example is encrypting in place over the array returned by KeyParameter.getKey(). The overwrite behavior occurs on JVMs that return a copy for JNI byte-array access rather than pinning the array.
What must happen for an attacker to obtain the AES key?
The application must subsequently transmit, store, or otherwise expose the output buffer after the aliasing call. In the affected case, that buffer can contain the raw AES key instead of the expected ciphertext, despite the call reporting the correct output length.
What can be done before upgrading?
Do not use the same Java array for the key, IV, or additional authenticated data and the destination buffer. Allocate and use a separate output array for encryption results.
How can this issue be identified in existing code or output?
Review calls to the affected native one-shot AES-CBC, CCM, CFB, CTR, GCM, or GCM-SIV packet ciphers for array aliasing between a read-only input and the output destination. The API does not signal the problem: the call returns the expected output length, so output inspection is needed to determine whether key bytes replaced ciphertext.