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🐛 detect dangerous patterns in toJSON() in dangerous workflows #4717

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🐛 detect dangerous patterns in toJSON() in dangerous workflows #4717

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4 changes: 3 additions & 1 deletion checks/raw/dangerous_workflow.go
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Original file line number Diff line number Diff line change
Expand Up @@ -52,7 +52,9 @@ func containsUntrustedContextPattern(variable string) bool {
if strings.Contains(variable, "github.head_ref") {
return true
}
return strings.Contains(variable, "github.event.") && untrustedContextPattern.MatchString(variable)
return strings.Contains(variable, "github.event.") &&
(untrustedContextPattern.MatchString(variable) ||
untrustedContextPattern.MatchString(fmt.Sprintf("toJSON(%s)", variable)))
Comment on lines +55 to +57
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@spencerschrock spencerschrock Sep 23, 2025

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this doesn't work as expected for the small example Pedro showed in his issue. I was curious about toJSON(github), which also ends up being vulnerable. But not every toJSON call would be vulnerable, only examples that are less specific. For example
toJSON(github.event.pull_request.state) should be declared as safe (though this is contrived)

Here's a patch with a test I was trying. As well as the example in my test repo (workflow now disabled):
https://github.com/spencerschrock/actions-test/actions/runs/17951418605/job/51051442328

diff --git a/checks/dangerous_workflow_test.go b/checks/dangerous_workflow_test.go
index 15befe75..58e4fb04 100644
--- a/checks/dangerous_workflow_test.go
+++ b/checks/dangerous_workflow_test.go
@@ -72,6 +72,15 @@ func TestDangerousWorkflow(t *testing.T) {
 				Score: checker.MaxResultScore,
 			},
 		},
+		{
+			name:          "toJSON injection is a failing score",
+			workflowPaths: []string{".github/workflows/github-workflow-dangerous-toJSON.yml"},
+			err:           nil,
+			expected: scut.TestReturn{
+				Score:        checker.MinResultScore,
+				NumberOfWarn: 2,
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
diff --git a/checks/testdata/.github/workflows/github-workflow-dangerous-toJSON.yml b/checks/testdata/.github/workflows/github-workflow-dangerous-toJSON.yml
new file mode 100644
index 00000000..c986aa08
--- /dev/null
+++ b/checks/testdata/.github/workflows/github-workflow-dangerous-toJSON.yml
@@ -0,0 +1,11 @@
+on:
+  pull_request_target:
+
+jobs:
+  get-pwned:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Log event and get pwned
+        run: |
+          echo '${{ toJSON(github.event) }}' | jq
+          echo '${{ toJSON(github) }}' | jq

}

type triggerName string
Expand Down
7 changes: 7 additions & 0 deletions checks/raw/dangerous_workflow_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ package raw
import (
"context"
"errors"
"fmt"
"io"
"os"
"testing"
Expand Down Expand Up @@ -83,6 +84,12 @@ func TestUntrustedContextVariables(t *testing.T) {
if r := containsUntrustedContextPattern(tt.variable); !r == tt.expected {
t.Fail()
}
if r := containsUntrustedContextPattern(fmt.Sprintf("toJSON(%s)", tt.variable)); !r == tt.expected {
t.Fail()
}
if r := containsUntrustedContextPattern(fmt.Sprintf("toJSON( %s )", tt.variable)); !r == tt.expected {
t.Fail()
}
})
}
}
Expand Down
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