Vulnerability · Published Aug 3, 2026 · Assigned by bcorg
CVE-2026-12803KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery)
High 8.7
In plain English
A high-severity security flaw in BC-JAVA from Legion of the Bouncy Castle Inc.. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 15% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 4.0)8.7High
Exploit odds (30 days)0.2%top 85.3% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | bouncycastle | no fix listed | DEBIAN-CVE-2026-12803 |
| Debian:13 | bouncycastle | no fix listed | DEBIAN-CVE-2026-12803 |
| Debian:14 | bouncycastle | 1.86-1 | DEBIAN-CVE-2026-12803 |
| Ubuntu:26.04:LTS | bouncycastle | no fix listed | UBUNTU-CVE-2026-12803 |
| Ubuntu:26.10 | bouncycastle | no fix listed | UBUNTU-CVE-2026-12803 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Legion of the Bouncy Castle Inc. | BC-JAVA | 0 – before 1.85 |
| Legion of the Bouncy Castle Inc. | BC-LTS-JAVA | 2.73.0 – before 2.73.12 |
Weakness: CWE-354 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber