# CVE-2026-59099

## Summary

- **CVE ID:** CVE-2026-59099
- **Severity:** CRITICAL
- **CVSS Score:** 9.3 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-323
- **Published:** Jul 2, 2026
- **Last Modified:** Jul 14, 2026

## Description

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.

## Affected Products

- apereo — cas (7.3.0)

## References

- [CNA](https://apereo.github.io/2026/06/18/vuln/)
- [CNA](https://github.com/apereo/cas/releases/tag/v8.0.0-RC6)
- [CNA](https://github.com/geo-chen/oss/blob/main/cas.md)
- [CNA](https://github.com/apereo/cas/commit/22c6f4adf738852782309b523b4e80371057f2d0)
- [CNA](https://www.vulncheck.com/advisories/apereo-cas-rc6-aes-gcm-nonce-reuse-information-disclosure)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.55%
- **EPSS Percentile:** 44.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._