CVE-2026-59640: In Bouncy Castle for Java before 1.85, OpenPGP CFB quick-check oracle active on symmetric/session-key paths

Q: How do I fix CVE-2026-59640?

bc-java: upgrade to 1.85; bcpg-fips: upgrade to 1.0.13, 2.0.13, 2.1.13; bouncy castle for java lts: upgrade to newer than 2.73.11. Exact commands for each OS are on this page.

Q: Is CVE-2026-59640 being exploited?

CVE-2026-59640 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-2026-59640 affect?

CVE-2026-59640 affects bc-java, bcpg-fips, bouncy castle for java lts. Severity is medium (CVSS 5.3). In Bouncy Castle for Java before 1.85, OpenPGP CFB quick-check oracle active on symmetric/session-key paths. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpg-fips 1.0.13

Q: How urgent is CVE-2026-59640?

Priority 31/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.3REMOTEUPGRADEUPGRADEUPGRADE

CVE-2026-59640 is a medium-severity flaw (CVSS 5.3) affecting bc-java, bcpg-fips, 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, OpenPGP CFB quick-check oracle active on symmetric/session-key paths. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpg-fips 1.0.13 (1.0.X series), 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series).

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 72%)
CISA exploited list	No
Weakness	CWE-203
Published	2026-08-03
Last modified	2026-08-28

Publisher (CNA): bcorg · Vendor: bouncycastle

Last updated 2026-08-28 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-03 01:16 UTCPublished CVE record published
2026-08-28 15:40 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 bcpg-fips UPGRADE

Affected: < 1.0.13 · >= 2.0.8 and < 2.0.13 · >= 2.1.10 and < 2.1.13

Fixed in: 1.0.13, 2.0.13, 2.1.13

Safe to downgrade to: a release before 2.0.8

1. Check installed version

apt-cache policy bcpg-fips || rpm -q bcpg-fips || bcpg-fips --version

2. UPGRADE to 1.0.13 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade bcpg-fips

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade bcpg-fips

Note

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

3. If no update is available yet, DOWNGRADE to a release before 2.0.8 (Debian / Ubuntu)

apt-cache madison bcpg-fips sudo apt install bcpg-fips=<VERSION_BEFORE_2.0.8> sudo apt-mark hold bcpg-fips

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list bcpg-fips sudo dnf downgrade bcpg-fips-<VERSION_BEFORE_2.0.8> sudo dnf versionlock add bcpg-fips

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-59640?

bc-java: upgrade to 1.85; bcpg-fips: upgrade to 1.0.13, 2.0.13, 2.1.13; bouncy castle for java lts: upgrade to newer than 2.73.11. Exact commands for each OS are on this page.

Is CVE-2026-59640 being exploited?

CVE-2026-59640 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-2026-59640 affect?

CVE-2026-59640 affects bc-java, bcpg-fips, bouncy castle for java lts. Severity is medium (CVSS 5.3). In Bouncy Castle for Java before 1.85, OpenPGP CFB quick-check oracle active on symmetric/session-key paths. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpg-fips 1.0.13

How urgent is CVE-2026-59640?

Priority 31/100. Remotely exploitable, no login, no user action

Software pages

Java vulnerabilities

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References

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