CVE-2026-63573Network attack vectorHinoki check available

Content decryption via CMS RSA padding oracle

Published Oct 2, 2026 · Updated Oct 2, 2026

CMS RSA key-transport padding oracle in Bouncy Castle C# .NET before 2.7.0 allows remote attackers to decrypt captured CMS content. KeyTransRecipientInformation.UnwrapKey rejects invalid PKCS#1 v1.5 padding with a distinct error instead of substituting a random content key, exposing a padding oracle. Exploitation requires a captured CMS message and repeated modified-message submissions to an application that decrypts with the recipient's private key and reveals distinguishable failures.

CVSS severityUnavailable
Unscored
EPSS probability0.31%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

CMS RSA key-transport padding oracle in Bouncy Castle C# .NET before 2.7.0 allows remote attackers to decrypt captured CMS content. KeyTransRecipientInformation.UnwrapKey rejects invalid PKCS#1 v1.5 padding with a distinct error instead of substituting a random content key, exposing a padding oracle. Exploitation requires a captured CMS message and repeated modified-message submissions to an application that decrypts with the recipient's private key and reveals distinguishable failures.

The record

CVE
CVE-2026-63573
Published
Oct 2, 2026
Updated
Oct 2, 2026
Vendor
Legion of the Bouncy Castle Inc.
Product
Bouncy Castle C# .NET
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 2, 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 <2.7.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Legion of the Bouncy Castle Inc. · Bouncy Castle C# .NETversion=0 <2.7.0

Published CVSS scores

No CVSS assessment is available in this record.

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.

Activity data is delayed. The latest report is Sep 28, 2026.

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

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

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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