CVE-2026-59639Network attack vector

Signature bypass via zero-signer CMS acceptance

Published Aug 3, 2026 · Updated Aug 3, 2026

Improper CMS signature verification in Bouncy Castle Java editions allows remote attackers to pass unsigned content as authentic. CMSSignedData.verifySignatures iterates an empty signer collection and returns true because neither its ASN.1 input layer nor SignerInformationStore rejects the empty set. Exploitation requires an application to accept attacker-supplied CMS/PKCS#7 data and trust that result without separately requiring an expected signer; affected releases include Java before 1.85, Java LTS 2.73.0 through 2.73.11, and BC-FJA 1.0.0 through 1.0.11, 2.0.0 through 2.0.11, and 2.1.0 through 2.1.11.

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

What happened

Improper CMS signature verification in Bouncy Castle Java editions allows remote attackers to pass unsigned content as authentic. CMSSignedData.verifySignatures iterates an empty signer collection and returns true because neither its ASN.1 input layer nor SignerInformationStore rejects the empty set. Exploitation requires an application to accept attacker-supplied CMS/PKCS#7 data and trust that result without separately requiring an expected signer; affected releases include Java before 1.85, Java LTS 2.73.0 through 2.73.11, and BC-FJA 1.0.0 through 1.0.11, 2.0.0 through 2.0.11, and 2.1.0 through 2.1.11.

The record

CVE
CVE-2026-59639
Published
Aug 3, 2026
Updated
Aug 3, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle Java
Classifications
CWE-347, CAPEC-475, T1553
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 FIPS Java APIversion=1.0.0 <1.0.12; version=2.0.0 <2.0.12; version=2.1.0 <2.1.12
Legion of the Bouncy Castle Inc. · Bouncy Castle Java LTSversion=2.73.0 <2.73.12

Published CVSS scores

8.7bcorgCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
7.5Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
CAPEC-475Signature Spoofing by Improper Validation
T1553Subvert Trust Controls

Public exploit references

No public exploit references are available in this record.

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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