CVE-2026-71884
In Bouncy Castle for Java LTS before 2.73.13, the native one-shot CTR packet cipher did not check that the requested input length fitted the counter space the IV left.
Overview
CVE-2026-71884 is a known-severity vulnerability. It was published on October 9, 2026.
Technical description
In Bouncy Castle for Java LTS before 2.73.13, the native one-shot CTR packet cipher did not check that the requested input length fitted the counter space the IV left. In CTR mode the IV and the block counter share one 16-byte block, so an IV of 13 to 15 bytes leaves a counter of only 1 to 3 bytes, addressing 256, 65536 or 16777216 blocks respectively. Given a longer input the counter wrapped and the keystream repeated from the start of the same packet, and the call then returned the full input length as though every byte had been correctly transformed. Two segments of the message were therefore encrypted under the same keystream, so their plaintexts can be recovered from the ciphertext alone, without the key, while the caller saw neither an exception nor a short length to indicate it. The streaming implementation validates at init and again while processing, and the portable AESCTRPacketCipher rejects such a request with "Counter in CTR/SIC mode out of range.", but the native one-shot
Remediation
Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
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Frequently asked questions
What is CVE-2026-71884?
CVE-2026-71884 is a known-severity vulnerability. It was published on October 9, 2026.
How severe is CVE-2026-71884?
CVSS score information is not yet available for this vulnerability. Check back as the CVE record is updated by NVD analysts.
How do I fix or remediate CVE-2026-71884?
Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-71884?
CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-71884 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.