apereo cas up to 8.0.0-RC5 Encryption Key nonce re-use

Summaryinfo

A vulnerability, which was classified as critical, has been found in apereo cas up to 8.0.0-RC5. This affects an unknown function of the component Encryption Key Handler. Performing a manipulation results in nonce re-use. This vulnerability is cataloged as CVE-2026-59099. It is possible to initiate the attack remotely. There is no exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in apereo cas up to 8.0.0-RC5. It has been classified as critical. This affects an unknown functionality of the component Encryption Key Handler. The manipulation with an unknown input leads to a nonce re-use vulnerability. CWE is classifying the issue as CWE-323. Nonces should be used for the present occasion and only once. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Apereo CAS 7.3.0 before 8.0.0-RC6 contains a cryptographic vulnerability that allows remote unauthenticated attackers to recover plaintext conversation state by exploiting AES-GCM initialization vector reuse across the server lifetime. Attackers can collect multiple client-side webflow execution tokens from the unauthenticated login page and perform known-plaintext analysis to decrypt the webflow conversation state due to keystream reuse caused by a fixed all-zero IV paired with the same encryption key.

The weakness was shared by George Chen. It is possible to read the advisory at apereo.github.io. This vulnerability is uniquely identified as CVE-2026-59099 since 07/02/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1600.001 according to MITRE ATT&CK.

Upgrading to version 8.0.0-RC6 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 22c6f4adf738852782309b523b4e80371057f2d0 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-41430). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• apereo

Name

• cas

Version

• 8.0.0-RC5

License

• open-source

Website

• Product: https://github.com/apereo/cas/

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Be aware that VulDB is the high quality source for vulnerability data.

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