CVE-2026-12816: In Bouncy Castle for Java before 1.85, IESEngine stream-mode MAC forgery via length-dependent KDF split

Q: How do I fix CVE-2026-12816?

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-2026-12816 being exploited?

CVE-2026-12816 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-2026-12816 affect?

CVE-2026-12816 affects bc-java, bouncy castle for java lts. Severity is high (CVSS 7.5). In Bouncy Castle for Java before 1.85, IESEngine stream-mode MAC forgery via length-dependent KDF split. This issue also affects Bouncy Castle for Java LTS before 2.73.12.

Q: How urgent is CVE-2026-12816?

Priority 33/100. High severity; Remotely exploitable, no login, no user action

Routine

HIGH 7.5REMOTEUPGRADEUPGRADE

CVE-2026-12816 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, IESEngine stream-mode MAC forgery via length-dependent KDF split. 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 93%)
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 14:38 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-2026-12816?

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-2026-12816 being exploited?

CVE-2026-12816 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-2026-12816 affect?

CVE-2026-12816 affects bc-java, bouncy castle for java lts. Severity is high (CVSS 7.5). In Bouncy Castle for Java before 1.85, IESEngine stream-mode MAC forgery via length-dependent KDF split. This issue also affects Bouncy Castle for Java LTS before 2.73.12.

How urgent is CVE-2026-12816?

Priority 33/100. High severity; Remotely exploitable, no login, no user action

Software pages

Java vulnerabilities

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References

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