cas: Reusing a Nonce, Key Pair in Encryption
CVE-2026-59099 is a critical-severity reusing a nonce, key pair in encryption vulnerability in cas from Apereo, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 8.0.0-RC6 as the first without the flaw, so updating cas to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.55% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update cas to 8.0.0-RC6 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CNA (vulncheck.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (vulncheck.com) |
| CVSS 3.1 | 9.1 | Critical | CNA (vulncheck.com) |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Reusing a Nonce, Key Pair in Encryption
Nonces should be used for the present occasion and only once.
How developers prevent this class of flaw
- Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
More Reusing a Nonce, Key Pair in Encryption vulnerabilities (CWE-323)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Other vulnerabilities in cas
- 7.5 High severity
- 7.5 High severity
- 9.8 Critical severity
- 8.1 High severity
- 7.5 High severity
Recent Reusing a Nonce, Key Pair in Encryption vulnerabilities
- 7.5 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 7.1 High severity
- 8.1 High severity
- 7.3 High severity
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