CVE-2026-12803: In Bouncy Castle for Java before 1.85, KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce

Q: How do I fix CVE-2026-12803?

bc-java: upgrade to 1.85; bouncy castle for java lts: upgrade to newer than 2.73.11. Exact commands for each OS are on this page.

Q: Is CVE-2026-12803 being exploited?

CVE-2026-12803 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-12803 affect?

CVE-2026-12803 affects bc-java, bouncy castle for java lts. Severity is high (CVSS 7.5). 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.

Q: How urgent is CVE-2026-12803?

Priority 35/100. High severity; Remotely exploitable, no login, no user action

Routine

HIGH 7.5REMOTEUPGRADEUPGRADE

CVE-2026-12803 is a high-severity flaw (CVSS 7.5) affecting bc-java, bouncy castle for java lts. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 85%)
CISA exploited list	No
Weakness	CWE-354
Published	2026-08-03
Last modified	2026-09-02

Publisher (CNA): bcorg · Vendor: bouncycastle

Last updated 2026-09-02 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-03 04:16 UTCPublished CVE record published
2026-09-02 14:37 UTCUpdated Record last modified

bouncycastle bc-java UPGRADE

Affected: < 1.85

Fixed in: 1.85

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy bc-java || rpm -q bc-java || bc-java --version

2. UPGRADE to 1.85 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade bc-java

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade bc-java

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

bouncycastle bouncy castle for java lts UPGRADE

Affected: <= 2.73.11

Fixed in: newer than 2.73.11

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy bouncy-castle-for-java-lts || rpm -q bouncy-castle-for-java-lts || bouncy-castle-for-java-lts --version

2. UPGRADE to newer than 2.73.11 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade bouncy-castle-for-java-lts

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade bouncy-castle-for-java-lts

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-12803?

bc-java: upgrade to 1.85; bouncy castle for java lts: upgrade to newer than 2.73.11. Exact commands for each OS are on this page.

Is CVE-2026-12803 being exploited?

CVE-2026-12803 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-12803 affect?

CVE-2026-12803 affects bc-java, bouncy castle for java lts. Severity is high (CVSS 7.5). 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.

How urgent is CVE-2026-12803?

Priority 35/100. High severity; Remotely exploitable, no login, no user action

Software pages

Java vulnerabilities

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References

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