Cryptographic Vulnerability in Apereo CAS Version 7.3.0
CVE-2026-59099

9.3CRITICAL

Key Information:

Vendor

Apereo

Status
Cas
Vendor
CVE Published:
2 July 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-59099?

Apereo CAS versions prior to 8.0.0-RC6 are susceptible to a cryptographic vulnerability that enables remote unauthenticated attackers to recover plaintext conversation state. This issue arises from AES-GCM initialization vector reuse, where the use of a constant all-zero IV in conjunction with a fixed encryption key compromises the security of webflow execution tokens. By exploiting this flaw, attackers can perform known-plaintext analysis on the tokens collected from the unauthenticated login page, effectively revealing sensitive conversation state across multiple client-side interactions. It is crucial for users of Apereo CAS to upgrade to the patched version to mitigate this risk.

Affected Version(s)

cas 7.3.0 < 8.0.0-RC6

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-59099 - Proof of Concept

References

https://apereo.github.io/2026/06/18/vuln/
vendor-advisory
https://github.com/apereo/cas/releases/tag/v8.0.0-RC6
release-notes
https://github.com/geo-chen/oss/blob/main/cas.md
technical-descriptionexploit

CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

George Chen
.