CVE-2026-5588: PKIX draft CompositeVerifier accepts empty signature sequence as valid.

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-15 · updated 2026-10-26
Weakness: CWE-327

Description

Use of a Broken or Risky Cryptographic Algorithm vulnerability in Legion of the Bouncy Castle Inc. BC-JAVA bcpkix on all (pkix modules), Legion of the Bouncy Castle Inc. BCPKIX-FIPS bcpkix on All (pkix modules), Legion of the Bouncy Castle Inc. BCPIX-LTS bcpkix on All (pkix modules). This vulnerability is associated with program files JcaContentVerifierProviderBuilder.Java, JcaContentVerfierProviderBuilder.Java. This issue affects BC-JAVA: from 1.67 before 1.80.2, from 1.81 before 1.81.1, from 1.82 before 1.84; BCPKIX-FIPS: from 2.0.6 before 2.0.11, from 2.1.7 before 2.1.11; BCPIX-LTS: from 2.73.7 before 2.73.11.

Affected products

Legion of the Bouncy Castle Inc. BC-JAVA: from 1.67 before 1.80.2; from 1.81 before 1.81.1; from 1.82 before 1.84 — fixed in 1.80.2, 1.81.1, 1.84
Legion of the Bouncy Castle Inc. BCPIX-LTS: from 2.73.7 before 2.73.11 — fixed in 2.73.11
Legion of the Bouncy Castle Inc. BCPKIX-FIPS: from 2.0.6 before 2.0.11; from 2.1.7 before 2.1.11 — fixed in 2.0.11, 2.1.11

How to fix

Upgrade to a fixed version: Legion of the Bouncy Castle Inc. BC-JAVA 1.80.2, 1.81.1, 1.84; Legion of the Bouncy Castle Inc. BCPIX-LTS 2.73.11; Legion of the Bouncy Castle Inc. BCPKIX-FIPS 2.0.11, 2.1.11. Check the vendor advisory for mitigations.

References

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