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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.

PUBLISHED Reserved 2026-07-02 | Published 2026-07-02 | Updated 2026-07-06 | Assigner VulnCheck




CRITICAL: 9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CRITICAL: 9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Problem types

Reusing a Nonce, Key Pair in Encryption

Product status

Default status
unaffected

7.3.0 (custom) before 8.0.0-RC6
affected

Credits

George Chen finder

References

apereo.github.io/2026/06/18/vuln/ (Maintainer Advisory) vendor-advisory

github.com/apereo/cas/releases/tag/v8.0.0-RC6 (Release Notes) release-notes

github.com/geo-chen/oss/blob/main/cas.md (Researcher Disclosure) technical-description exploit

github.com/...ommit/22c6f4adf738852782309b523b4e80371057f2d0 (Fix Commit) patch

www.vulncheck.com/...-gcm-nonce-reuse-information-disclosure third-party-advisory

cve.org (CVE-2026-59099)

nvd.nist.gov (CVE-2026-59099)

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