---
title: "CVE-2026-71888: Bouncy Castle - Authentication Bypass"
description: "Bouncy Castle for Java < 1.86 contains an authentication bypass caused by inconsistent handling of digestAlgorithm and authAttrs fields in CMS AuthenticatedData parser, letting attackers modify authenticated attributes without key access, exploit requires message modification in transit."
url: https://panop.io/threat-heartbeat/CVE-2026-71888/
---

# CVE-2026-71888 Bouncy Castle - Authentication Bypass

Bouncy Castle for Java < 1.86 contains an authentication bypass caused by inconsistent handling of digestAlgorithm and authAttrs fields in CMS AuthenticatedData parser, letting attackers modify authenticated attributes without key access, exploit requires message modification in transit.

CVSS base score 8.7 /10

High

CISA KEV

Not listed

Public exploit

None known

EPSS

0.11% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-71888)

## Details

Type

Authentication Bypass

Impact

Privilege Escalation

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-354](https://cwe.mitre.org/data/definitions/354.html)

## Vendor fix

Update to Bouncy Castle for Java 1.86 or later, or respective fixed versions in LTS and FIPS series.

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-2026-71888](https://nvd.nist.gov/vuln/detail/CVE-2026-71888)
- [https://github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95](https://github.com/bcgit/bc-java/commit/dcb683b32b440f1beb1d2276a34930164281fb95)
- [https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888](https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071888)

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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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