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 ↗

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

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

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