---
title: "CVE-2026-71890: Bouncy Castle - Broken Access Control"
description: "Bouncy Castle for Java < 1.86 contains a broken access control vulnerability caused by improper validation of MLS external commit Remove proposals in Group.validateExternalCachedProposals, letting external joiners evict arbitrary group members and take over their slots, exploit requires crafted external commit with Remove proposal."
url: https://panop.io/threat-heartbeat/CVE-2026-71890/
---

# CVE-2026-71890 Bouncy Castle - Broken Access Control

Bouncy Castle for Java < 1.86 contains a broken access control vulnerability caused by improper validation of MLS external commit Remove proposals in Group.validateExternalCachedProposals, letting external joiners evict arbitrary group members and take over their slots, exploit requires crafted external commit with Remove proposal.

CVSS base score 8.7 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.25% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-71890)

## Details

Type

Broken Access Control

Impact

Broken Access Control

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/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

Published

3 October 2026

Updated

15 October 2026

Weakness

[CWE-863](https://cwe.mitre.org/data/definitions/863.html)

## Vendor fix

Update to version 1.86 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-71890](https://nvd.nist.gov/vuln/detail/CVE-2026-71890)
- [https://github.com/bcgit/bc-java/commit/7e8bb10eb90baddf3f10b8679f627462b9522d24](https://github.com/bcgit/bc-java/commit/7e8bb10eb90baddf3f10b8679f627462b9522d24)
- [https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071890](https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071890)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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