VDB-385487 · CVE-2026-12803 · GCVE-0-2026-12803

Legion of the Bouncy Castle Bouncy Castle for Java/Bouncy Castle for Java LTS prior 1.85/2.73.12 KCCMBlockCipher MAC signature verification

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
5.2	$0-$5k	2.48

Summaryinfo

A vulnerability marked as problematic has been reported in Legion of the Bouncy Castle Bouncy Castle for Java and Bouncy Castle for Java LTS. This vulnerability affects unknown code of the component KCCMBlockCipher MAC. The manipulation leads to signature verification. This vulnerability is uniquely identified as CVE-2026-12803. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Legion of the Bouncy Castle Bouncy Castle for Java and Bouncy Castle for Java LTS. It has been rated as problematic. This issue affects an unknown code of the component KCCMBlockCipher MAC. The manipulation with an unknown input leads to a signature verification vulnerability. Using CWE to declare the problem leads to CWE-347. The product does not verify, or incorrectly verifies, the cryptographic signature for data. Impacted is integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-12803 since 06/21/2026. The exploitation is known to be easy. The attack may be initiated remotely. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 1.85 or 2.73.12 eliminates this vulnerability.

Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

Programming Language Software

Vendor

Legion of the Bouncy Castle

Name

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.4
VulDB Meta Temp Score: 5.2

VulDB Base Score: 5.4
VulDB Temp Score: 5.2
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AV	AC	Au	C	I	A
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳
💳	💳	💳	💳	💳	💳

Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock
Unlock	Unlock	Unlock	Unlock	Unlock	Unlock

VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Signature verification
CWE: CWE-347 / CWE-345
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Bouncy Castle for Java/Bouncy Castle for Java LTS 1.85/2.73.12

Timelineinfo

06/21/2026 CVE reserved
08/03/2026 +43 days Advisory disclosed
08/03/2026 +0 days VulDB entry created
08/03/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-12803 (🔒)
GCVE (CVE): GCVE-0-2026-12803
GCVE (VulDB): GCVE-100-385487

Entryinfo

Created: 08/03/2026 06:17
Changes: 08/03/2026 06:17 (55)
Complete: 🔍
Cache ID: 216::103