CVE-2026-5426
CWE-321Published: April 16, 2026· Updated: Apr 18, 2026
Official 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
Risk Analysis
Digital Knowledge KnowledgeDeliver deployments are vulnerable due to a hard-coded ASP.NET/IIS machineKey value, which allows attackers to bypass ViewState validation and achieve remote code execution. The CVSS score of 7.5 indicates a high severity, and confirmed exploitation in the wild makes this a critical issue. This flaw enables malicious ViewState deserialization attacks.
This vulnerability is actively being exploited in the wild and is included in CISA's KEV catalog. It is remotely exploitable with low attack complexity, allowing unauthenticated attackers to achieve remote code execution.
Update Digital Knowledge KnowledgeDeliver deployments to a version released after February 24, 2026. Ensure that ASP.NET/IIS machineKey values are unique and securely generated for each deployment.
Technical Analysis
CVE-2026-5426 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.
A successful exploit results in complete confidentiality breach (data exposure), with a CVSS base score of 7.5.
CISA has added CVE-2026-5426 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
CVSS v3.1 Vector Breakdown
Exploit & PoC Resources
News & Research Mentioning CVE-2026-5426
A now-patched high-severity security flaw affecting Digital Knowledge KnowledgeDeliver, a Learning Management System (LMS) popular in Japan, was exploited as a zero-day to deliver the Godzilla web shell and ultimately facilitate the deployment of Cobalt Strike Beacon. The vulnerability, tracked as CVE-2026-5426 (CVSS score: 7.5), stems from the use of hard-coded ASP.NET machine keys, leading to [xlite_meta score:59 src:The Hacker News xlite_fp:9b71c8d831996f692f95e7e3ed1aff7865f491294fc599054bd5fc52e5952675]
Written by: Takahiro Sugiyama, Peter Revelant, Mathew Potaczek Introduction In late 2025, Mandiant responded to a security incident involving a compromised web server running KnowledgeDeliver. KnowledgeDeliver is a Learning Management System (LMS) developed by Digital Knowledge commonly used in Japan. Mandiant identified a critical vulnerability that allowed unauthenticated Remote Code Execution (RCE). An unknown threat actor leveraged this access to inject malicious code into the LMS platform, with the goal of infecting users visiting the site. This vulnerability stems from the use of identical pre-shared ASP.NET machine keys across multiple customer deployments. The vulnerability was initially exploited as a zero-day, now tracked as CVE-2026-5426. The Vulnerability KnowledgeDeliver installations deployed before Feb. 24, 2026 relied on a standardized web.config file provided by the vendor. This configuration file contained hardcoded machineKey values used by the ASP.NET framework to e
All References (2)
Quick Facts
Related CVEs (CWE-321)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2026-5426 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1