.NET CVE-2026-21665

Deserialization of Untrusted Data (CWE-502)

2026-02-23 support@hackerone.com

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Vulnerability Assessment

Weakness	CWE CWE-502 MITRE ATT&CK 2 techniques across 2 tactics: Execution, Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	Exploitation no authentication required. Exploitable via remote/network.
Exploit ScenarioDerived	A remote attacker without authentication could exploit this vulnerability to compromise the affected system.

This Week Schedule remediation this week. Why: No CVSS yet + dangerous CWE (RCE/injection/auth-bypass class).

No patch listed yet 0.4% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

RemediationAI

Monitor vendor advisories for a patch.

Affected ProductsAI

The Print Service component of Fiserv Originate Loans Peripherals (formerly Velocity Services) in unsupported version 2021.2.4 (build 4.7.3155.0011) u

Affects your stack

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Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Classified as CWE-502 (Deserialization of Untrusted Data). The Print Service component of Fiserv Originate Loans Peripherals (formerly Velocity Services) in unsupported version 2021.2.4 (build 4.7.3155.0011) uses deprecated .NET Remoting TCP channels that allow unsafe deserialization of untrusted data. When these services are exposed to an untrusted network in a client-managed deployment, an unauthenticated attacker can achieve remote code execution. Version 2021.2.4 is no longer supported by Fiserv. Customers should upgrade to a currently supported rel

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Exploit and PoC references, threat intelligence from 22 sources

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DescriptionCVE.org

The Print Service component of Fiserv Originate Loans Peripherals (formerly Velocity Services) in unsupported version 2021.2.4 (build 4.7.3155.0011) uses deprecated .NET Remoting TCP channels that allow unsafe deserialization of untrusted data. When these services are exposed to an untrusted network in a client-managed deployment, an unauthenticated attacker can achieve remote code execution. Version 2021.2.4 is no longer supported by Fiserv. Customers should upgrade to a currently supported release (2025.1 or later) and ensure that .NET Remoting service ports are not exposed beyond trusted network boundaries.

This CVE documents behavior observed in a client-hosted deployment running an unsupported legacy version of Originate Loans Peripherals with .NET Remoting ports exposed to an untrusted network. This is not a default or supported configuration. Customers running legacy versions should upgrade to a currently supported release and ensure .NET Remoting ports are restricted to trusted network segments. The finding does not apply to Fiserv-hosted environments.

Threat Intelligence Overview

EPSS Score

0.4%

Top 39% exploitable

Data Quality

2 sources

Confidence: Low

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity Not scored yet

CISA KEV No

Public POC No

EPSS 0.4%

Patch available No

Active threat No

Deciding rule

No CVSS yet + dangerous CWE (RCE/injection/auth-bypass class)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

Attack Technique

Insecure Deserialization CRITICAL

Insecure deserialization occurs when an application converts serialized data (a stream of bytes representing an object's state) back into a living object without proper validation.

Remote Code Execution CRITICAL

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.