CVE-2026-5426

HighRCE

Published: 16 April 2026

Published

16 April 2026

Modified

18 April 2026

KEV Added

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Patch

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CVSS Score 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Score 0.0007 20.3th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-5426 is a high-severity Use of Hard-coded Cryptographic Key (CWE-321) vulnerability in Co (inferred from references). Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 20.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SC-12 (Cryptographic Key Establishment and Management) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Directly remediates the hard-coded machineKey flaw by identifying, reporting, and applying vendor updates released on or after February 24, 2026.

SC-12 Cryptographic Key Establishment and Management good match

prevent

Establishes and manages cryptographic keys securely, prohibiting hard-coded keys that enable ViewState validation bypass.

SI-10 Information Input Validation partial match

prevent

Validates untrusted inputs like ViewState data to mitigate deserialization attacks even if cryptographic weaknesses exist.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

Hard-coded machineKey enables unauthenticated remote exploitation of public-facing ASP.NET/IIS web app for RCE via ViewState deserialization, directly mapping to T1190.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

Hard-coded ASP.NET/IIS machineKey value in Digital Knowledge KnowledgeDeliver deployments prior to February 24, 2026 allows adversaries to circumvent ViewState validation mechanisms and achieve remote code execution via malicious ViewState deserialization attacks

Deeper analysisAI

CVE-2026-5426 involves a hard-coded ASP.NET/IIS machineKey value in Digital Knowledge KnowledgeDeliver deployments prior to February 24, 2026. This cryptographic weakness, published on 2026-04-16, enables adversaries to bypass ViewState validation mechanisms, facilitating remote code execution through malicious ViewState deserialization attacks. The vulnerability carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) and maps to CWE-321 (Use of Hard-coded Cryptographic Key) and CWE-502 (Deserialization of Untrusted Data).

Attackers can exploit this vulnerability remotely over the network with low attack complexity, requiring no authentication, privileges, or user interaction. Successful exploitation allows unauthenticated adversaries to submit crafted malicious ViewState data, circumventing validation due to the static machineKey and achieving arbitrary remote code execution on the targeted server, primarily impacting confidentiality.

Mitigation guidance is available in the Mandiant vulnerability disclosure at https://github.com/mandiant/Vulnerability-Disclosures/blob/master/2026/MNDT-2026-0009.md and on the vendor's Digital Knowledge KnowledgeDeliver product page at https://www.digital-knowledge.co.jp/product/kd/. Deployments prior to February 24, 2026 remain vulnerable, indicating that updates released on or after that date address the hard-coded key issue.