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Add explicit strict-mode policy for pull_request_target checkouts #66649

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Merged
pelikhan merged 8 commits into from
Oct 7, 2026
Merged

Add explicit strict-mode policy for pull_request_target checkouts #66649

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03c6c87
Initial plan
Copilot Oct 7, 2026
46f9703
Support explicit pull_request_target trusted checkout policy
Copilot Oct 7, 2026
e8e3f44
Nest pull_request_target checkout policy
Copilot Oct 7, 2026
089aeb9
docs: add draft ADR-66649 for explicit pull_request_target trusted ch…
github-actions[bot] Oct 7, 2026
79c1b9d
Reject fetch refs in trusted pull request target checkouts
Copilot Oct 7, 2026
53d8277
Formalize pull request target checkout policy
Copilot Oct 7, 2026
07dcc81
Merge remote-tracking branch 'origin/main' into copilot/support-stric…
Copilot Oct 7, 2026
a4a8674
Refresh checkout refs and golden expectations after main merge
Copilot Oct 7, 2026
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Reject fetch refs in trusted pull request target checkouts 
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
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@pelikhan
Copilot and pelikhan authored Oct 7, 2026
commit 79c1b9d72834684ce9e05c8095f7372a6cb25cd3
2 changes: 1 addition & 1 deletion docs/src/content/docs/reference/checkout.md
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Expand Up @@ -194,7 +194,7 @@ checkout:
current: true
```

`on.pull_request_target.allowed-checkouts` defaults to no additional trusted checkouts. Each entry requires a literal `owner/repository` and a non-empty literal branch, tag, or commit SHA. Matching is exact and case-sensitive; repository/ref pairs cannot be combined across entries. Expressions, wildcards, and `refs/pull/...` refs are rejected in the policy. Every configured checkout must independently satisfy the policy or the existing base-checkout rules. External repositories with omitted or PR-dependent refs remain rejected. Wiki checkouts are not covered by this allowlist.
`on.pull_request_target.allowed-checkouts` defaults to no additional trusted checkouts. Each entry requires a literal `owner/repository` and a non-empty literal branch, tag, or commit SHA. Matching is exact and case-sensitive; repository/ref pairs cannot be combined across entries. Expressions, wildcards, and `refs/pull/...` refs are rejected in the policy. Every configured checkout must independently satisfy the policy or the existing base-checkout rules. Do not configure `checkout.fetch` for these checkouts: follow-up fetches can add refs beyond the trusted checkout, so they do not satisfy the policy. External repositories with omitted or PR-dependent refs remain rejected. Wiki checkouts are not covered by this allowlist.

`on.pull_request_target.acknowledge-risk` defaults to `false`. Setting it to `true` suppresses **only** the strict-mode dangerous-trigger warning, including for `checkout: false` or a supported base checkout. It neither allows other checkouts nor disables unrelated warnings, strict validation, or safe-update checks. An allowlist without acknowledgment still emits the trigger warning.

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10 changes: 1 addition & 9 deletions pkg/workflow/checkout_input_render.go
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Expand Up @@ -4,8 +4,6 @@ import (
"fmt"
"strconv"
"strings"

"github.com/goccy/go-yaml"
)

func (cm *CheckoutManager) defaultCheckoutIndex(entry *resolvedCheckout) int {
Expand Down Expand Up @@ -48,13 +46,7 @@ func (cm *CheckoutManager) writeDefaultCheckoutInputs(sb *strings.Builder, overr
}

func writeCheckoutRef(sb *strings.Builder, ref string) {

@github-actions github-actions Bot Oct 7, 2026

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L50: shrink: YAML unmarshal-and-compare solely to decide quoting. Always use strconv.Quote(ref); checkout refs are strings and that preserves every literal while removing the parser branch.

Copilot AI Oct 7, 2026

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writeCheckoutRef now always uses strconv.Quote(ref); the YAML unmarshal-and-compare branch is removed. Commit: 79c1b9d7.

// Preserve literal refs that YAML would otherwise interpret as numbers or indicators.
value := ref
var scalar any
if err := yaml.Unmarshal([]byte(ref), &scalar); err != nil || scalar != ref {
value = strconv.Quote(ref)
}
fmt.Fprintf(sb, " ref: %s\n", value) //nolint:fprintferrorunchecked // strings.Builder writes cannot fail.
fmt.Fprintf(sb, " ref: %s\n", strconv.Quote(ref)) //nolint:fprintferrorunchecked // strings.Builder writes cannot fail.
}

func writeCheckoutDepthAndSparse(sb *strings.Builder, entry *resolvedCheckout) {
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4 changes: 2 additions & 2 deletions pkg/workflow/pull_request_target_validation.go
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Expand Up @@ -191,7 +191,7 @@ func hasOnlyTrustedPullRequestTargetCheckouts(configs []*CheckoutConfig, allowed
}

func isAllowedPullRequestTargetCheckout(cfg *CheckoutConfig, allowedCheckouts []any) bool {
if cfg == nil || cfg.Wiki {
if cfg == nil || cfg.Wiki || len(cfg.Fetch) > 0 {
return false
}
// Fail closed even when called without schema validation. Never allow expressions
Expand All @@ -216,7 +216,7 @@ func isAllowedPullRequestTargetCheckout(cfg *CheckoutConfig, allowedCheckouts []
}

func isTrustedPullRequestTargetCheckout(cfg *CheckoutConfig) bool {
if cfg == nil {
if cfg == nil || len(cfg.Fetch) > 0 {
return false
}

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4 changes: 4 additions & 0 deletions pkg/workflow/pull_request_target_validation_test.go
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Expand Up @@ -469,6 +469,9 @@ func TestPullRequestTargetPolicy(t *testing.T) { //nolint:largefunc // Table cov
{name: "head repository expression", policy: acknowledged + allowlist, checkout: strings.ReplaceAll(externalCheckout, "dotnet/AspNetCore.Docs", "${{ github.event.pull_request.head.repo.full_name }}"), errorContains: insecureCheckout},
{name: "head ref expression", policy: acknowledged + allowlist, checkout: strings.ReplaceAll(externalCheckout, "ref: main", "ref: ${{ github.event.pull_request.head.sha }}"), errorContains: insecureCheckout},
{name: "base ref expression for external repository", policy: acknowledged + allowlist, checkout: strings.ReplaceAll(externalCheckout, "ref: main", "ref: ${{ github.event.pull_request.base.ref }}"), errorContains: insecureCheckout},
{name: "allowlisted checkout with PR fetch ref", policy: acknowledged + allowlist, checkout: externalCheckout + " fetch: [refs/pull/123/head]\n", errorContains: insecureCheckout},
{name: "allowlisted checkout with fetch expression", policy: acknowledged + allowlist, checkout: externalCheckout + " fetch: [\"${{ github.event.pull_request.head.ref }}\"]\n", errorContains: insecureCheckout},
{name: "trusted base checkout with additional fetch", policy: acknowledged, checkout: "checkout:\n repository: ${{ github.repository }}\n ref: ${{ github.event.pull_request.base.sha }}\n fetch: [\"refs/pulls/open/*\"]\n", errorContains: insecureCheckout},
{name: "mixed allowed and untrusted checkouts", policy: acknowledged + allowlist, checkout: externalCheckout + " - ref: ${{ github.event.pull_request.head.sha }}\n path: untrusted\n", errorContains: insecureCheckout},
{name: "policy cannot allow repository expression", policy: acknowledged + strings.ReplaceAll(allowlist, "dotnet/AspNetCore.Docs", "${{ github.event.pull_request.head.repo.full_name }}"), checkout: externalCheckout, errorContains: "'repository'"},
{name: "policy cannot allow ref expression", policy: acknowledged + strings.ReplaceAll(allowlist, "ref: main", "ref: ${{ github.event.pull_request.head.sha }}"), checkout: externalCheckout, errorContains: "'ref'"},
Expand Down Expand Up @@ -597,6 +600,7 @@ func TestAllowedPullRequestTargetCheckoutFailsClosed(t *testing.T) {
{Repository: "dotnet/AspNetCore.Docs", Ref: "${{ github.event.pull_request.head.sha }}"},
{Repository: "dotnet/AspNetCore.Docs", Ref: "refs/pull/123/head"},
{Repository: "dotnet/AspNetCore.Docs", Ref: "refs/pull/123/merge"},
{Repository: "dotnet/AspNetCore.Docs", Ref: "main", Fetch: []string{"refs/pull/123/head"}},
{Repository: "dotnet/*", Ref: "main"},
{Repository: "dotnet/AspNetCore.Docs", Ref: ""},
{Repository: "dotnet/AspNetCore.Docs", Ref: "main", Wiki: true},
Expand Down
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