CVE-2026-59099
CVE-2026-59099 is a critical-severity vulnerability with a CVSS 3.x base score of 9.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-323.
Key facts
- Severity: Critical (CVSS 3.x base score 9.1)
- CVSS v4: 9.3
- EPSS exploit prediction: 0% (28th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-323
- Published:
- Last modified:
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.
Frequently asked questions
- What is 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.
- How severe is CVE-2026-59099?
- CVE-2026-59099 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
- Is CVE-2026-59099 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (28th percentile), an estimate of the probability of exploitation in the next 30 days.
- How do I fix CVE-2026-59099?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
- When was CVE-2026-59099 published?
- CVE-2026-59099 was published on 2026-07-02 and last updated on 2026-07-06.
References
- https://apereo.github.io/2026/06/18/vuln/
- https://github.com/apereo/cas/commit/22c6f4adf738852782309b523b4e80371057f2d0
- https://github.com/apereo/cas/releases/tag/v8.0.0-RC6
- https://github.com/geo-chen/oss/blob/main/cas.md
- https://www.vulncheck.com/advisories/apereo-cas-rc6-aes-gcm-nonce-reuse-information-disclosure
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