# CVE-2026-12803: KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery)

> CVE-2026-12803: KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery). CVSS 7.5 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-12803
Last updated: 2026-09-02T14:37:53Z

- Published: 2026-08-03 02:52 UTC · Updated: 2026-09-02 14:37 UTC · Assigner: bcorg
- CVSS: 7.5 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS: 0.24%, 15th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-354

## Description

In Bouncy Castle for Java before 1.85, KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery). This issue also affects Bouncy Castle for Java LTS before 2.73.12.

## Affected vendors and products

- Legion of the Bouncy Castle Inc.: BC-JAVA
- Legion of the Bouncy Castle Inc.: BC-LTS-JAVA

## Tracked companies

- [Confluence](https://rewindex.com/company/confluence.md)
- [Jira](https://rewindex.com/company/jira.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-12803)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-12803)
- [https://github.com/bcgit/bc-java/commit/697794413ebf7bc5e3fce609a707826ba52981af](https://github.com/bcgit/bc-java/commit/697794413ebf7bc5e3fce609a707826ba52981af)
- [https://github.com/bcgit/bc-java/commit/7d79aa76e984da85f2a541cae8ba2ae56e1713bc](https://github.com/bcgit/bc-java/commit/7d79aa76e984da85f2a541cae8ba2ae56e1713bc)
- [https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9012803](https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9012803)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-12803 · Markdown: https://rewindex.com/cve/CVE-2026-12803.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-12803 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T04:04:51.731Z