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

Quick assessment

Affected
Legion of the Bouncy Castle Inc. BC-JAVA
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Bouncy Castle Java是Legion of the Bouncy Castle Inc开源的一个加密算法程序。 Bouncy Castle Java 1.49至1.84之前版本存在安全漏洞，该漏洞源于使用有缺陷的加密算法，可能导致接受空签名序列为有效。

CVSS 6.3 · Medium EPSS 0.69% · P51

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle

Affected Version Matrix 6

VendorProduct Version RangeStatus
Legion of the Bouncy Castle Inc. BC-JAVA 1.67< 1.80.2 affected
1.81< 1.81.1 affected
1.82< 1.84 affected
Legion of the Bouncy Castle Inc. BCPIX-LTS 2.73.7< 2.73.11 affected
Legion of the Bouncy Castle Inc. BCPKIX-FIPS 2.0.6< 2.0.11 affected
2.1.7< 2.1.11 affected
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I. Basic Information for CVE-2026-5588

Vulnerability Information
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Vulnerability Title
PKIX draft CompositeVerifier accepts empty signature sequence as valid.
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber
Source: CVE Program / CVE List V5
Vulnerability Type
使用已被攻破或存在风险的密码学算法
Source: CVE Program / CVE List V5
Vulnerability Title
Bouncy Castle Java 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Bouncy Castle Java是Legion of the Bouncy Castle Inc开源的一个加密算法程序。 Bouncy Castle Java 1.49至1.84之前版本存在安全漏洞，该漏洞源于使用有缺陷的加密算法，可能导致接受空签名序列为有效。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Legion of the Bouncy Castle Inc. BC-JAVA 1.67 ~ 1.80.2 -
Legion of the Bouncy Castle Inc. BCPKIX-FIPS 2.0.6 ~ 2.0.11 -
Legion of the Bouncy Castle Inc. BCPIX-LTS 2.73.7 ~ 2.73.11 -

II. Public POCs for CVE-2026-5588

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III. Intelligence Information for CVE-2026-5588

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Patches & Fixes for CVE-2026-5588 (1)

Same Patch Batch · Legion of the Bouncy Castle Inc. · 2026-04-15 · 5 CVEs total

CVE-2025-14813 9.3 CRITICAL GOSTCTR implementation unable to process more than 255 blocks correctly
CVE-2026-5598 8.9 HIGH Non-constant time comparisons risk private key leakage in FrodoKEM.
CVE-2026-3505 8.7 HIGH Unbounded PGP AEAD chunk size leads to pre-auth resource exhaustion.
CVE-2026-0636 5.5 MEDIUM LDAP Injection Vulnerability in LDAPStoreHelper.java

IV. Related Vulnerabilities

Same product: BC-JAVA
Same vendor: Legion of the Bouncy Castle Inc.
Same weakness: CWE-327

V. Comments for CVE-2026-5588

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