CVE-2026-71884
Reusing a Nonce, Key Pair in Encryption
Published Oct 9, 2026 · corrected/updated Oct 15, 2026 · evidence confidence high
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.
Grounded briefings
Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.
Executive
CVE-2026-71884 is a high public vulnerability record for this product. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.
System administrator
Identify whether this product is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: org.bouncycastle:bcprov-debug-lts8on; org.bouncycastle:bcprov-lts8on. Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.
Security analyst
Signals on file: CVSS 8.2, EPSS 0.4%. It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-323. Sources contributing to this record: cve_org, epss, nvd, snyk. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.
Exploitation and remediation
Exploitation evidence
Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.
Patch and remediation
No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.
Safe detection guidance
Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Oct 14, 2026 · Snyk Vulnerability Database
Detected
Reusing a Nonce, Key Pair in Encryption
Oct 15, 2026 · NIST NVD
Updated
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
Affected
- maven org.bouncycastle:bcprov-debug-lts8onversion unspecified
- maven org.bouncycastle:bcprov-lts8onversion unspecified
Sources
- CVE.orgVulnerability recordCVE-2026-71884
Official CVE identifier
cve.org - FIRST EPSSExploitation probabilityCVE-2026-71884
30-day exploitation probability 0.4%
first.org - NIST NVDVulnerability recordCVE-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. 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
nvd.nist.gov - Snyk Vulnerability DatabasePackage advisorySNYK-JAVA-ORGBOUNCYCASTLE-20828170
Reusing a Nonce, Key Pair in Encryption
security.snyk.io - Snyk Vulnerability DatabasePackage advisorySNYK-JAVA-ORGBOUNCYCASTLE-20828171
Reusing a Nonce, Key Pair in Encryption
security.snyk.io