HighCVE-2026-71886

OpenPGP certification accepted from a subkey without certification authority (CVE-2026-71886)

Published 03.10.2026Last modified 05.10.2026Sources: BSI, CVE.org, SUSE

What is affected, what to do

Update Legion of the Bouncy Castle BC-JAVA to version 1.86.

Affected: Legion of the Bouncy Castle BC-JAVA lt 1.81..1.86
Fixed in: Legion of the Bouncy Castle BC-JAVA 1.86

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Metrics

8.2

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: Vendor (CNA), CVSS v4

8.2

CVSS v4

Severity High on the scale from 0 to 10.

Source: BSI, CVE.org, SUSE

0.2 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 5.9

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 71.28 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 8.2 Methodology
CVSS v4 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 8.2
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.2 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 5.9; Low — this CVE sits in the lower 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 03.10.2026
CISA assessment (SSVC): Exploitation: none known · not automatable · Technical impact: partial; Source: CISA Vulnrichment, as of 5 October 2026
CWE CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect. Read in glossary: CWE-863, CWE-285

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

In Bouncy Castle for Java before 1.86, the high-level OpenPGP certificate API accepted a third-party certification or trust delegation from any component key of the issuing certificate, without requiring that component to have been granted the authority to certify. OpenPGPCertificate.getCertificationBy() and getDelegationBy() resolve a third-party signature by matching its issuer key identifier against every key of the third-party certificate, then verify the issuing component's binding chain and the signature itself; nothing checked that the issuing component carried the RFC 9580 sec. 5.2.3.29 certification key flag (CERTIFY_OTHER) when the signature was created. A subkey bound only with SIGN_DATA - the online signing subkey of exactly the offline-primary arrangement those key flags exist to express - could therefore issue a positive User ID certification over an attacker-controlled identity, or a full-trust depth-one direct-key delegation of introducer trust, and the API returned it as a valid signature chain attributed to the third-party certificate. An application treating getCertificationBy(...).isValid() or getDelegationBy(...) as an identity or trusted-introducer decision would attribute the attacker's assertion to the offline primary key. The same held for a legacy RSA subkey bound only for encryption, whose algorithm is nonetheless able to sign. This does not forge the primary key's signature or recover any private key; it promotes an already-compromised restricted subkey to the primary key's identity-issuing authority, defeating the containment the key-flag separation provides. A third-party certification or delegation is now attributed to the issuing certificate only when the component key that made it is the primary key, or is a subkey holding CERTIFY_OTHER when the signature was created, so certification-capable subkeys continue to be accepted; primary keys are accepted whatever their key flags say, since a primary key is certification-capable by construction and certificates carrying no key flags subpacket at all are common. Third-party revocations are deliberately outside the rule, since declining to honour one would keep trust alive rather than withdraw it.

Source: BSI WID Portal, BSI CSAF, NVD (NIST), cvelistv5, suse_csaf

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Legion of the Bouncy Castle Inc.	BC-JAVA	`1.81 – < 1.86`	`1.86`
Open Source	Bouncy Castle Java	`< 1.86`	`1.86`
Open Source	Bouncy Castle Java LTS	`< 2.73.13`	`2.73.13`

Vendors and products

Weakness classes (CWE)

CWE-863Incorrect Authorization
Class
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Entry at MITRE CWE-863
CWE-285Improper Authorization
Class
The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
Entry at MITRE CWE-285

References & sources

github.combcgit/bc-java/wiki/CVE‐2026‐71886Vendor advisory
github.combcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fbPatch

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

05.10.2026Record modifiedCISA ADP

CISA assessment (SSVC): exploitation: none known, automatable: no

Show the original change

Individual changes of this event as published by NVD
Type	Action	Before	After
SSVC assessment	added	—	{"id":"CVE-2026-71886","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-05T16:02:59.243532Z"}

Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

03.10.2026Receivedbcorg

CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber

Weakness type: CWE-285, CWE-863

Description added or changed

New references:

Show 7 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Description	added	—	In Bouncy Castle for Java before 1.86, the high-level OpenPGP certificate API accepted a third-party certification or trust delegation from any component key of the issuing certificate, without requiring that component to have been granted the authority to certify. OpenPGPCertificate.getCertificationBy() and getDelegationBy() resolve a third-party signature by matching its issuer key identifier against every key of the third-party certificate, then verify the issuing component's binding chain and the signature itself; nothing checked that the issuing component carried the RFC 9580 sec. 5.2.3.29 certification key flag (CERTIFY_OTHER) when the signature was created. A subkey bound only with SIGN_DATA - the online signing subkey of exactly the offline-primary arrangement those key flags exist to express - could therefore issue a positive User ID certification over an attacker-controlled identity, or a full-trust depth-one direct-key delegation of introducer trust, and the API returned it as a valid signature chain attributed to the third-party certificate. An application treating getCertificationBy(...).isValid() or getDelegationBy(...) as an identity or trusted-introducer decision would attribute the attacker's assertion to the offline primary key. The same held for a legacy RSA subkey bound only for encryption, whose algorithm is nonetheless able to sign. This does not forge the primary key's signature or recover any private key; it promotes an already-compromised restricted subkey to the primary key's identity-issuing authority, defeating the containment the key-flag separation provides. A third-party certification or delegation is now attributed to the issuing certificate only when the component key that made it is the primary key, or is a subkey holding CERTIFY_OTHER when the signature was created, so certification-capable subkeys continue to be accepted; primary keys are accepted whatever their key flags say, since a primary key is certification-capable by construction and certificates carrying no key flags subpacket at all are common. Third-party revocations are deliberately outside the rule, since declining to honour one would keep trust alive rather than withdraw it.
CVSS	added	—	AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
Weakness type (CWE)	added	—	CWE-285
Weakness type (CWE)	added	—	CWE-863
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/71xxx/CVE-2026-71886.json">CVE-2026-71886</a>
Reference	added	—	https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb
Reference	added	—	https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071886

Source identifier: 91579145-5d7b-4cc5-b925-a0262ff19630

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