CVE-2026-71885 Bouncy Castle - Authentication Bypass

Bouncy Castle for Java < 1.86 contains a broken authentication caused by improper binding of X.509 credentials to LeafNode signature_key in MLS implementation, letting unauthenticated attackers impersonate others and decrypt group messages, exploit requires deployment admitting external commits without independent credential checks.

CVSS base score 9.2 /10
Critical
CISA KEV
Not listed
Public exploit
None known
EPSS
0.19% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Privilege Escalation, Information Disclosure, Data Tampering
CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/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-287

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

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