What is CVE-2026-12803?

CVE-2026-12803 is a high-severity vulnerability in Bouncycastle Bc-Java, classified under Improper Validation of Integrity Check Value. CVSS score: 7.5/10. Published 2026-08-03.

How severe is CVE-2026-12803?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Bouncycastle Bc-Java

CVE-2026-12803

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.

Published 2026-08-03 · last modified 2026-09-02.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (14.7th percentile), scored 2026-11-04.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 14.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Bouncycastle Bc-Java
Bouncycastle Bouncy Castle For Java Lts
Legion Of The Bouncy Castle Inc. Bc-Java — versions 0
Legion Of The Bouncy Castle Inc. Bc-Lts-Java — versions 2.73.0

Weakness classification (CWE)

CWE-354 — Improper Validation of Integrity Check Value

References

91579145-5d7b-4cc5-b925-a0262ff19630 (vendor-advisory)
91579145-5d7b-4cc5-b925-a0262ff19630 (Patch, patch)
91579145-5d7b-4cc5-b925-a0262ff19630 (Patch, patch)
91579145-5d7b-4cc5-b925-a0262ff19630 (vendor-advisory, Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2026-12803?: CVE-2026-12803 is a high-severity vulnerability in Bouncycastle Bc-Java, classified under Improper Validation of Integrity Check Value. CVSS score: 7.5/10. Published 2026-08-03.
How severe is CVE-2026-12803?: High severity. CVSS v3 base score is 7.5 out of 10.