CVE-2026-12803Public exploitNetwork attack vector

AEAD forgery via nonce-independent KCCM tags

Published Aug 3, 2026 · Updated Aug 3, 2026

AEAD authentication bypass in Bouncy Castle Java before 1.85 and Java LTS before 2.73.12 allows attackers to forge KCCM ciphertexts. When AAD is empty, processPacket skips processAAD, leaving the nonce-bearing G1 block outside the CBC-MAC and making each tag depend only on the key and plaintext. Exploitation requires a chosen-plaintext encryption oracle and three queries; accepted forgeries break message integrity without disclosing plaintext.

CVSS severity8.7
High
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

AEAD authentication bypass in Bouncy Castle Java before 1.85 and Java LTS before 2.73.12 allows attackers to forge KCCM ciphertexts. When AAD is empty, processPacket skips processAAD, leaving the nonce-bearing G1 block outside the CBC-MAC and making each tag depend only on the key and plaintext. Exploitation requires a chosen-plaintext encryption oracle and three queries; accepted forgeries break message integrity without disclosing plaintext.

The record

CVE
CVE-2026-12803
Published
Aug 3, 2026
Updated
Aug 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
CWE-354
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <1.85

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle Javaversion=0 <1.85
Legion of the Bouncy Castle Inc. · Bouncy Castle Java LTSversion=2.73.0 <2.73.12

Published CVSS scores

8.7Legion of the Bouncy Castle Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-354Improper Validation of Integrity Check Value

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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