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CVE-2021-25740 is a Kubernetes confused deputy issue arising from the design of the Endpoints and EndpointSlice APIs. Users with permission to create or modify Endpoints or EndpointSlice objects can manually specify backend IP addresses rather than relying solely on controller-managed pod backends. In clusters using shared Ingress controllers or LoadBalancer implementations, this allows an attacker to repoint a Service they control so that the shared networking component forwards traffic to IPs or workloads in other namespaces or other otherwise unreachable locations. The issue is architectural rather than an implementation bug in a single function: Kubernetes Services expose a stable identity, while EndpointSlice/Endpoints store the actual backend addresses, and many networking components trust those objects when selecting forwarding targets. Kubernetes has stated this behavior is a fundamental feature used by existing tooling and operators, so the issue is considered not fully patchable without breaking core functionality.
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No public exploit code observed for this vulnerability.
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14 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An unfixed Kubernetes design flaw in Endpoints and EndpointSlice that enables cross-namespace forwarding by manually specifying IP addresses for LoadBalancer or Ingress backends.
A Kubernetes vulnerability in which users able to modify Endpoint or EndpointSlice objects can redirect ingress or LoadBalancer traffic to addresses they should not be able to access, enabling bypass of network security controls in certain multi-tenant cluster architectures.
Another unpatchable Kubernetes vulnerability referenced as part of the same series, but not described in detail in this content.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.