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CVE Record

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

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.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Affected Bouncy Castle PKIX code can incorrectly treat an empty composite-signature sequence as valid. In applications relying on this draft composite-signature verification, an attacker may bypass authenticity checks and cause untrusted data to be accepted as genuine. The cited CVSS score is 7.5, reflecting high integrity impact without confidentiality or availability impact.

Executive priority

Prioritize investigation and remediation for internet-facing trust, identity, certificate, signing, or validation services using affected bcpkix versions. The potential outcome is authenticity bypass with high integrity impact. Systems not using draft composite-signature verification may have lower practical exposure, but dependency presence and code-path reachability should be verified promptly rather than assumed.

Technical view

CVE-2026-5588 affects bcpkix CompositeVerifier behavior in specified BC-JAVA, BCPKIX-FIPS, and BCPIX-LTS releases. An empty signature sequence can pass verification, creating an improper cryptographic-verification outcome associated with CWE-327 and CWE-347. The supplied vector is network-accessible, low-complexity, unauthenticated, and requires no user interaction, although practical reachability depends on application use of the affected path.

Likely exposure

Exposure is most likely where Java applications use affected bcpkix versions to verify draft composite signatures derived from untrusted or remotely supplied PKIX data. Merely having Bouncy Castle installed does not establish reachability. Direct and transitive dependencies, runtime-loaded versions, and actual CompositeVerifier call paths must be examined.

Exploitation context

The source bundle does not cite active exploitation, and the CVE is not listed as KEV. The CVSS vector indicates potentially remote, unauthenticated exploitation when an application exposes the vulnerable verification path. Evidence supplied here does not establish exploit prevalence, affected application configurations, or successful attacks in the wild.

Researcher notes

The issue is tied to JcaContentVerifierProviderBuilder.java and the corresponding FIPS-named builder in the supplied record. Researchers should distinguish package presence from reachable CompositeVerifier use and examine version resolution at runtime. The cited patch and vendor advisory support fixed-version analysis; the bundle provides no evidence of active exploitation or broader cryptographic primitives being affected.

Mitigation direction

  • Upgrade BC-JAVA to an applicable fixed release: 1.80.2, 1.81.1, or 1.84.
  • Upgrade BCPKIX-FIPS to 2.0.11 or 2.1.11, according to the deployed release branch.
  • Upgrade BCPIX-LTS to 2.73.11 or later vendor-confirmed fixed release.
  • Apply applicable Red Hat errata when using affected distribution packages.
  • Review vendor guidance before using compensating controls where immediate upgrading is impossible.

Validation and detection

  • Inventory direct and transitive bcpkix dependencies across builds, deployed artifacts, and runtime classpaths.
  • Confirm runtime versions fall outside every affected range listed in the CVE record.
  • Identify whether applications invoke composite-signature verification on externally supplied PKIX data.
  • Add a negative regression test confirming an empty composite-signature sequence is rejected.
  • Re-scan rebuilt artifacts and verify applicable Red Hat package updates are installed.
Prepared
Confidence
high
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-327: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-347: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-5588 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
18Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N3.93.6redhat-SADP
6.3CVSS 4.0MediumCVSS: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——bcorg

Vulnerability scoring details

Base CVSS 4.0 score

6.3Medium
CVSS 4.0 vector shape for CVE-2026-5588Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPbouncycastle: BC-JAVA: PKIX draft CompositeVerifier accepts empty signature sequence as valid
other:Red Hat severity ratingcvssV3_1
  • 2026-04-15T10:00:59.672Z: Reported to Red Hat.
  • 2026-04-15T09:06:15.617Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Legion of the Bouncy Castle Inc.BC-JAVAbcpkix, 1.67, 1.81, 1.82unaffected
Legion of the Bouncy Castle Inc.BCPKIX-FIPSbcpkix, 2.0.6, 2.1.7unaffected
Legion of the Bouncy Castle Inc.BCPIX-LTSbcpkix, 2.73.7unaffected
Weakness

CWE details

CWE-327CWE-347

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-327 · source CWE mapping

Use of a Broken or Risky Cryptographic Algorithm

Use of a Broken or Risky Cryptographic Algorithm represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-347 · source CWE mapping

Improper Verification of Cryptographic Signature

Improper Verification of Cryptographic Signature represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs