CVE-2026-59099Public exploitNetwork attack vector

Conversation-state disclosure via fixed AES-GCM initialization vector

Published Jul 2, 2026 · Updated Jul 2, 2026

Cryptographic nonce reuse in Apereo CAS 7.3.0 before 8.0.0-RC6 allows remote attackers to recover webflow conversation state. BaseBinaryCipherExecutor.buildParameterSpec() supplies one all-zero IV for every AES-GCM encryption under the server key, causing client-side execution tokens to reuse a keystream. The unauthenticated login page exposes enough tokens for known-plaintext analysis that reveals encrypted conversation data.

CVSS severity9.3
Critical
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cryptographic nonce reuse in Apereo CAS 7.3.0 before 8.0.0-RC6 allows remote attackers to recover webflow conversation state. BaseBinaryCipherExecutor.buildParameterSpec() supplies one all-zero IV for every AES-GCM encryption under the server key, causing client-side execution tokens to reuse a keystream. The unauthenticated login page exposes enough tokens for known-plaintext analysis that reveals encrypted conversation data.

The record

CVE
CVE-2026-59099
Published
Jul 2, 2026
Updated
Jul 2, 2026
Vendor
Apereo
Product
Apereo CAS
Classifications
CWE-323
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 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=7.3.0 <8.0.0-RC6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Apereo · Apereo CASversion=7.3.0 <8.0.0-RC6

Published CVSS scores

9.1VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/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-323Reusing a Nonce, Key Pair in Encryption

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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