Vulnerability in Apereo Cas
CVE-2026-59099
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.005 (43.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 44th percentile — 43.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000
Affected products
- Apereo Cas — versions 7.3.0
Weakness classification (CWE)
References
- apereo.github.io/2026/06/18/vuln/ (vendor-advisory)
- github.com/apereo/cas/commit/22c6f4adf738852782309b523b4e80371057f2d0 (patch)
- github.com/apereo/cas/releases/tag/v8.0.0-RC6 (release-notes)
- github.com/geo-chen/oss/blob/main/cas.md (technical-description, exploit)
- www.vulncheck.com/advisories/apereo-cas-rc6-aes-gcm-nonce-reuse-information-dis… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-59099?
- CVE-2026-59099 is a critical-severity vulnerability in Apereo Cas, classified under Reusing a Nonce, Key Pair in Encryption. CVSS score: 9.1/10. Published 2026-07-02.
- How severe is CVE-2026-59099?
- Critical severity. CVSS v3 base score is 9.1 out of 10.