Add application-controlled security policies for kubeconfig exec plugins by Copilot · Pull Request #1930 · kubernetes-client/csharp

Copilot · 2026-10-06T21:51:05Z

Untrusted kubeconfigs can launch arbitrary local processes through exec credential plugins. This adds application-controlled authorization without requiring callers to parse and inspect kubeconfig themselves.

Policy API: Immutable AllowAll (default), DenyAll, and Allowlist policies across configuration builders, including Classic and AOT. Existing API signatures remain available.
Enforcement: Checks initial execution and token refresh before process launch. Denials throw ExecCredentialPluginDeniedException; kubeconfig cannot override the application policy.
Allowlist semantics: Match basenames or exact absolute paths, including Windows UNC paths. Empty lists deny all; invalid entries and quoted commands are rejected. Allowlist mode also rejects kubeconfig-supplied environment overrides to prevent command redirection and loader injection.
Trust boundaries: Basenames permit any matching executable location. Arguments and executable contents are not restricted; the policy is not a sandbox.

var config = KubernetesClientConfiguration.BuildConfigFromConfigFile(
    kubeConfigPath,
    execCredentialPluginPolicy: ExecCredentialPluginPolicy.DenyAll);

// Or explicitly approve credential plugins:
var config = KubernetesClientConfiguration.BuildConfigFromConfigFile(
    kubeConfigPath,
    execCredentialPluginPolicy: ExecCredentialPluginPolicy.Allowlist(
        "kubelogin",
        @"C:\Program Files\Contoso\trusted-plugin.exe"));

Fixes Add security policy support for kubeconfig exec credential plugins #1918

Copilot

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linux-foundation-easycla · 2026-10-06T21:51:13Z

✅ login: brendandburns / name: Brendan Burns (0157b92, 36876d0, 506e755, 6b8c21d, 8525843, b270f4f)
❌ - login: @Copilot / name: Copilot Autofix powered by AI. The commit (506e755) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.
❌ - login: @Copilot / name: copilot-swe-agent[bot]. The commit (0157b92, 36876d0, 53692ed, 6b8c21d, 8525843, b270f4f) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

Co-authored-by: brendandburns <5751682+brendandburns@users.noreply.github.com>

kubernetes-prow · 2026-10-06T22:01:06Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Copilot

Copilot review overview

🟡 Changes recommended

Kubeconfig-controlled environment variables can bypass allowlisted command restrictions and still enable arbitrary code execution.

Review effort: Balanced
Findings: 1

Open (1)

Allowlist ignores kubeconfig-controlled environment during execution · New

Co-authored-by: brendandburns <5751682+brendandburns@users.noreply.github.com>

Copilot

Copilot review overview

🔵 Needs a closer look

Security-sensitive process execution changes span multiple target variants, while the PR explicitly indicates build and security validation remain incomplete.

Review effort: Balanced
Findings: 1

Open (1)

Allowlist ignores kubeconfig-controlled environment during execution

brendandburns · 2026-10-14T16:01:40Z

@copilot can you add documentation that this is intended for defense in depth and is not a hard security boundary, loading a kubeconfig from an untrusted source is an inherently dangerous activity and should be handled as part of an overall security model, not relying exclusively on this capability.

Co-authored-by: brendandburns <5751682+brendandburns@users.noreply.github.com>

Copilot · 2026-10-14T16:03:36Z

@copilot can you add documentation that this is intended for defense in depth and is not a hard security boundary, loading a kubeconfig from an untrusted source is an inherently dangerous activity and...

Added the README clarification in commit 36876d0: the policy is defense in depth, not a hard security boundary, and untrusted kubeconfigs must be addressed within the application's overall security model.

Copilot

🔵 Needs a closer look

Basename validation incorrectly rejects valid Unix executable names containing colons.

1 open finding

Allowlist ignores kubeconfig-controlled environment during execution

Previously missed (1)

In code that hasn't changed since last review

Rejects valid Unix executable basenames containing colons

src/KubernetesClient/ExecCredentialPluginPolicy.cs:93

The unconditional ':' check rejects valid Unix executable basenames such as plugin:v2, even though the API accepts command basenames and colon is only special for Windows drive syntax. Restrict the colon check to Windows so valid Unix basenames can be allowlisted.

🧠 Review effort: Balanced

Co-authored-by: brendandburns <5751682+brendandburns@users.noreply.github.com>

Copilot

🟡 Changes recommended

DenyAll can probe untrusted network paths, and Windows casing differences can reject approved executables.

2 open issues

1 resolved since last review

Allowlist ignores kubeconfig-controlled environment during execution

_{Review effort: Balanced}

+            return commands.Any(entry =>
+                TryResolveCommand(entry, path, out var resolvedEntry) &&
+                string.Equals(resolvedEntry, resolvedCommand, StringComparison.Ordinal));


Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

🟡 Changes recommended

Executable resolution permits unchecked fallback searches and unapproved network probes, and uses incompatible Windows extension rules.

3 open issues

1 previously missed issue

In code that hasn't changed since last review

Respect native Windows extension resolution rules

src/KubernetesClient/ExecCredentialPluginPolicy.cs:209

On Windows, PATHEXT controls shell lookup, but CreateRunnableExternalProcess uses UseShellExecute = false. Native process creation appends .exe to an extensionless command; this resolver can instead select a preceding .com, .bat, or .cmd and pin it into FileName. Enabling an allowlist can therefore launch a different executable or fail on a batch shim where the original command would find an .exe. Use native process-creation extension rules and add a Windows test with competing extensions.

1 resolved since last review

Avoid resolving commands when the policy allows none

_{Review effort: Balanced}

+            return TryResolveCommand(command, Environment.GetEnvironmentVariable("PATH"), out var resolvedCommand)
+                ? resolvedCommand
+                : command;


+            try
+            {
+                var fullPath = Path.GetFullPath(command);
+                if (!File.Exists(fullPath))


brendandburns · 2026-10-19T17:35:36Z

@copilot There are some common environment variables used for exec (e.g. AWS_PROFILE) so I think that blocking all environment variables won't work. Can you focus on just blocking dangerous ones and allowing others

Co-authored-by: brendandburns <5751682+brendandburns@users.noreply.github.com>

Copilot · 2026-10-19T17:43:59Z

@copilot There are some common environment variables used for exec (e.g. AWS_PROFILE) so I think that blocking all environment variables won't work. Can you focus on just blocking dangerous ones and a...

Allowlist mode now blocks PATH, dynamic-loader variables, and common language-runtime injection variables while allowing ordinary overrides such as AWS_PROFILE. Added coverage and updated the README in commit 0157b92.

Copilot

🟡 Changes recommended

Unblocked startup environment variables allow code injection through approved credential plugins.

4 open issues

_{Review effort: Balanced}

+                string.Equals(name, "_JAVA_OPTIONS", StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(name, "JDK_JAVA_OPTIONS", StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(name, "CLASSPATH", StringComparison.OrdinalIgnoreCase) ||
+                string.Equals(name, "DOTNET_STARTUP_HOOKS", StringComparison.OrdinalIgnoreCase));


Initial plan

53692ed

Copilot AI assigned Copilot and brendandburns Oct 6, 2026

Copilot AI balanced review requested due to automatic review settings October 6, 2026 21:51

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Copilot started work on behalf of brendandburns October 6, 2026 21:51

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Copilot AI linked an issue Oct 6, 2026 that may be closed by this pull request

Add security policy support for kubeconfig exec credential plugins #1918

Open

Add application-controlled exec credential plugin policies

8525843

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Copilot AI balanced review requested due to automatic review settings October 6, 2026 22:01

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Comment thread src/KubernetesClient/ExecCredentialPluginPolicy.cs Outdated

Harden exec allowlists against quoted commands and environment injection

b270f4f

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Copilot AI balanced review requested due to automatic review settings October 6, 2026 22:22

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Copilot AI changed the title ~~[WIP] Add security policy support for kubeconfig exec credential plugins~~ Add application-controlled security policies for kubeconfig exec plugins Oct 6, 2026

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Document exec policy defense-in-depth limits

36876d0

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Copilot AI balanced review requested due to automatic review settings October 14, 2026 16:03

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Copilot started work on behalf of brendandburns October 16, 2026 23:37

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Match exec allowlist to kuberc command resolution

6b8c21d

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Copilot AI balanced review requested due to automatic review settings October 16, 2026 23:47

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Improve command validation logic in ExecCredentialPluginPolicy

506e755

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Copilot AI balanced review requested due to automatic review settings October 19, 2026 16:14

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This was referenced Oct 19, 2026

Add exec credential plugin policy (kuberc credentialPluginPolicy parity) kubernetes-client/javascript#3109

Draft

Add exec credential plugin policy (kuberc credentialPluginPolicy semantics) kubernetes-client/java#4951

Draft

Copilot started work on behalf of brendandburns October 19, 2026 17:36

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Allow safe exec environment overrides

0157b92

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Copilot AI balanced review requested due to automatic review settings October 19, 2026 17:40

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