Legion of the Bouncy Castle Bouncy Castle for Java up to 2.73.12 Native One-Shot CTR Packet Cipher input validation

Summaryinfo

A vulnerability has been found in Legion of the Bouncy Castle Bouncy Castle for Java up to 2.73.12 and classified as critical. This affects an unknown function of the component Native One-Shot CTR Packet Cipher. The manipulation leads to input validation. This vulnerability is referenced as CVE-2026-71884. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Legion of the Bouncy Castle Bouncy Castle for Java up to 2.73.12. This issue affects an unknown part of the component Native One-Shot CTR Packet Cipher. The manipulation with an unknown input leads to a input validation vulnerability. Using CWE to declare the problem leads to CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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 path has a single entry point and performed no counter-range validation there. It now preflights the IV-derived counter range and rejects an over-long request before any output is written, so the operation is failure-atomic and never reports success for bytes it did not correctly transform. A counter of four bytes or more cannot be exhausted by a Java int length and is unaffected, as is a full 16-byte IV, where the counter range is the caller's responsibility. Bouncy Castle for Java (bcprov) is not affected, as it ships no native implementations.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-71884 since 08/08/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 2.73.13 eliminates this vulnerability.

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Productinfo

Type

• Programming Language Software

Vendor

• Legion of the Bouncy Castle

Name

• Bouncy Castle for Java

Version

• 2.73.0
• 2.73.1
• 2.73.2
• 2.73.3
• 2.73.4
• 2.73.5
• 2.73.6
• 2.73.7
• 2.73.8
• 2.73.9
• 2.73.10
• 2.73.11
• 2.73.12

CPE 2.3info

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CPE 2.2info

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