CVE-2026-12803
KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery)
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.
INFO
Published Date :
Aug. 3, 2026, 4:16 a.m.
Last Modified :
Aug. 3, 2026, 4:16 a.m.
Remotely Exploit :
Yes !
Source :
91579145-5d7b-4cc5-b925-a0262ff19630
Affected Products
The following products are affected by CVE-2026-12803
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | HIGH | 91579145-5d7b-4cc5-b925-a0262ff19630 | ||||
| CVSS 4.0 | HIGH | 91579145-5d7b-4cc5-b925-a0262ff19630 |
Solution
- Update Bouncy Castle for Java to version 1.85 or later.
- Update Bouncy Castle for Java LTS to version 2.73.12 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-12803.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-12803 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-12803
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-12803 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-12803 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 91579145-5d7b-4cc5-b925-a0262ff19630
Aug. 03, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://github.com/bcgit/bc-java', 'vendor': 'Legion of the Bouncy Castle Inc.', 'modules': ['core'], 'product': 'BC-JAVA', 'versions': [{'status': 'affected', 'version': '0', 'lessThan': '1.85', 'versionType': 'maven'}], 'platforms': ['all'], 'packageURL': 'pkg:maven/org.bouncycastle/bcprov-jdk18on', 'packageName': 'bcprov', 'programFiles': ['KCCMBlockCipher'], 'collectionURL': 'https://www.bouncycastle.org/download/bouncy-castle-java/', 'defaultStatus': 'unaffected'}, {'repo': 'https://github.com/bcgit/bc-lts-java', 'vendor': 'Legion of the Bouncy Castle Inc.', 'modules': ['core'], 'product': 'BC-LTS-JAVA', 'versions': [{'status': 'affected', 'version': '2.73.0', 'lessThan': '2.73.12', 'versionType': 'maven'}], 'platforms': ['all'], 'packageURL': 'pkg:maven/org.bouncycastle/bcprov-lts8on', 'packageName': 'bcprov-lts8on', 'programFiles': ['KCCMBlockCipher'], 'collectionURL': 'https://www.bouncycastle.org/download/bouncy-castle-java-lts/', 'defaultStatus': 'unaffected'}] Added 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. Added CVSS V4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber Added CWE CWE-354 Added Reference https://github.com/bcgit/bc-java/commit/697794413ebf7bc5e3fce609a707826ba52981af Added Reference https://github.com/bcgit/bc-java/commit/7d79aa76e984da85f2a541cae8ba2ae56e1713bc Added Reference https://github.com/bcgit/bc-java/wiki/CVE-2026-12803