CVE-2026-59099: Apereo CAS 7.3.0 < 8.0.0-RC6 - AES-GCM Nonce Reuse Information Disclosure

Synopsis

An AES-GCM nonce-reuse cryptographic vulnerability exists in Apereo CAS versions 7.3.0 through 8.0.0-RC6. The server reuses a fixed all-zero initialization vector with the same encryption key across its entire lifetime, meaning any unauthenticated remote attacker who collects multiple webflow execution tokens from the login page can perform known-plaintext analysis and recover the plaintext conversation state. Successful exploitation gives the attacker read access to confidential session state and the ability to tamper with authentication conversation data. A patched-image rebuild at version 8.0.0-RC6 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Apereo CAS login page over the network; exposure to any network-accessible instance is sufficient since the vulnerable endpoint is the unauthenticated login flow.

• AuthenticationNot required

  No credentials or account are needed; the vulnerability is exploitable entirely through the public-facing unauthenticated login page.

• Victim interactionNot required

  The attacker collects webflow execution tokens by interacting directly with the server; no victim user action is required.

• Attack complexityDetail

  Exploitation is reliable and condition-free once multiple tokens are collected; no race conditions or memory-layout dependencies are involved.

Blast Radius

• Attacker decrypts webflow conversation state, reading confidential in-progress authentication session data such as credential fragments and identity assertions in transit.
• Attacker recovers keystream material reusable to forge or modify encrypted conversation tokens, allowing manipulation of the authentication flow state.
• Exposed conversation state may reveal service ticket targets, authentication context, and user-supplied credential inputs submitted during the login process.