CVE-2025-66631 — Csla
Fix: MarimerLLC/csla#4018CVE-2025-66631 is a Deserialization of Untrusted Data vulnerability in Csla. A fix is available for Csla — see the affected versions and patch details below.
CSLA .NET is vulnerable to Remote Code Execution via WcfProxy
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-66631.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
CslaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Versions of CSLA .NET prior to version 6 allow the use of WcfProxy. WcfProxy uses the NetDataContractSerializer (NDCS) which has known vulnerabilities that can allow remote execution of code during deserialization. NDCS itself is considered obsolete, and you should avoid using WcfProxy or upgrade to CSLA 6 or higher where this issue does not exist.
Patches
CSLA .NET version 6 and higher do not use WCF or NetDataContractSerializer.
Workarounds
If you are using a version CSLA .NET older than version 6, you should stop using WcfProxy in your data portal configuration. Doing this avoids the use of WCF and the NetDataContractSerializer, avoiding the vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Csla | all versions | 6.0.0dotnet add package Csla --version 6.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Csla, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update Csla to 6.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-66631 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-66631 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-66631. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-66631 in your dependencies?
O3 Security finds CVE-2025-66631 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.