How severe is CVE-2026-59639?

CVE-2026-59639 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-59639 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-59639?

CVE-2026-59639 primarily affects Bouncycastle Bc-java. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-59639?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-59639 published?

CVE-2026-59639 was published on 2026-08-03 and last updated on 2026-08-28.

CVE-2026-59639

CVE-2026-59639 is a high-severity vulnerability in Bouncycastle Bc-java with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-347.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (6th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-347
Affected product: Bouncycastle Bc-java
Published: 2026-08-03
Last modified: 2026-08-28

Description

In Bouncy Castle for Java before 1.85, CMS verifySignatures returns true for SignedData with zero signers. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.12 (1.0.X series), 2.0.12 (2.0.X series) and 2.1.12 (2.1.X series).

Frequently asked questions

What is CVE-2026-59639?: In Bouncy Castle for Java before 1.85, CMS verifySignatures returns true for SignedData with zero signers. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.12 (1.0.X series), 2.0.12 (2.0.X series) and 2.1.12 (2.1.X series).
How severe is CVE-2026-59639?: CVE-2026-59639 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-59639 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-59639?: CVE-2026-59639 primarily affects Bouncycastle Bc-java. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-59639?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-59639 published?: CVE-2026-59639 was published on 2026-08-03 and last updated on 2026-08-28.

References

Affected products (3)

cpe:2.3:a:bouncycastle:bc-java:*:*:*:*:*:*:*:*
cpe:2.3:a:bouncycastle:bcpkix-fips:*:*:*:*:*:*:*:*
cpe:2.3:a:bouncycastle:bouncy_castle_for_java_lts:*:*:*:*:*:*:*:*

More vulnerabilities in Bouncycastle Bc-java

CVE-2007-6721 — Critical (CVSS 10.0): The Legion of the Bouncy Castle Java Cryptography API before release 1.38, as used in Crypto Provider Package before…
CVE-2018-1000613 — Critical (CVSS 9.8): Legion of the Bouncy Castle Legion of the Bouncy Castle Java Cryptography APIs 1.58 up to but not including 1.60…
CVE-2026-58062 — Critical (CVSS 9.1): In Bouncy Castle for Java before 1.85, Stapled OCSP response accepted without binding to the checked certificate. This…
CVE-2026-8763 — Critical (CVSS 9.1): In Bouncy Castle for Java before 1.85, Name Constraints bypass via trailing dot in rfc822Name and URI. This issue also…
CVE-2026-59650 — Critical (CVSS 9.1): In Bouncy Castle for Java before 1.85, MTI/A0 DH agreement exponentiates unvalidated peer value. This issue also…
CVE-2026-12817 — High (CVSS 8.6): In Bouncy Castle for Java before 1.85, OpenPGP AEAD decryption skips final tag on chunk-aligned data. This issue also…

All CVEs affecting Bouncycastle Bc-java →

Other CWE-347 (Improper Verification of Cryptographic Signature) vulnerabilities

CVE-2026-5430 — Critical (CVSS 10.0): The JWT authentication mechanism accepts tokens signed with algorithms other than those explicitly configured or…
CVE-2026-56451 — Critical (CVSS 10.0): A vulnerability has been identified in Opcenter X (All versions < V2604). Affected applications do not properly…
CVE-2026-48558 — Critical (CVSS 10.0): SimpleHelp versions 5.5.15 and prior and 6.0 pre-release versions contain an authentication bypass vulnerability in the…
CVE-2023-25574 — Critical (CVSS 10.0): `jupyterhub-ltiauthenticator` is a JupyterHub authenticator for learning tools interoperability (LTI).…
CVE-2024-45409 — Critical (CVSS 10.0): The Ruby SAML library is for implementing the client side of a SAML authorization. Ruby-SAML in <= 12.2 and 1.13.0 <=…
CVE-2024-32962 — Critical (CVSS 10.0): xml-crypto is an xml digital signature and encryption library for Node.js. In affected versions the default…

Browse all CWE-347 (Improper Verification of Cryptographic Signature) vulnerabilities →