fix: argument injection in git archive fallback (CWE-88) (#49500)

* Initial plan

* Plan: fix argument injection in downloadWorkflowContentViaGit

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

* fix: argument injection in downloadWorkflowContentViaGit (CWE-88)

Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: pelikhan <4175913+pelikhan@users.noreply.github.com>
Co-authored-by: Peli de Halleux <pelikhan@users.noreply.github.com>

Author: Copilot

pkg/cli/download_workflow.go

@@ -28,14 +28,25 @@ func downloadWorkflowContentViaGit(ctx context.Context, repo, path, ref string,
 
 	downloadLog.Printf("Attempting git fallback for downloading workflow content: %s/%s@%s", repo, path, ref)
 
+	if err := gitutil.ValidateGitRef(ref); err != nil {
+		return nil, fmt.Errorf("refusing git fallback: %w", err)
+	}
+	if err := gitutil.ValidateGitPath(path); err != nil {
+		return nil, fmt.Errorf("refusing git fallback: %w", err)
+	}
+
 	// Use git archive to get the file content without cloning
 	githubHost := getGitHubHostForRepo(repo)
 	repoURL := fmt.Sprintf("%s/%s.git", githubHost, repo)
 
-	// git archive command: git archive --remote=<repo> <ref> <path>
+	// git archive command: git archive --remote=<repo> <ref> -- <path>
+	// The '--' end-of-options separator ensures path is never parsed as a git flag
+	// even if it begins with '-' (argument injection, CWE-88).
+	// ValidateGitRef/ValidateGitPath above guard against leading '-' and '..' at
+	// this layer; '--' is kept as defence-in-depth per the git(1) specification.
 	// #nosec G204 -- repoURL, ref, and path are from workflow import configuration authored by the
 	// developer; exec.CommandContext with separate args (not shell execution) prevents shell injection.
-	cmd := exec.CommandContext(ctx, "git", "archive", "--remote="+repoURL, ref, path)
+	cmd := exec.CommandContext(ctx, "git", "archive", "--remote="+repoURL, ref, "--", path)
 	archiveOutput, err := cmd.Output()
 	if err != nil {
 		downloadLog.Printf("git archive failed, falling back to git clone: repo=%s, ref=%s, err=%v", repo, ref, err)

pkg/cli/download_workflow_test.go

@@ -3,6 +3,7 @@
 package cli
 
 import (
+	"context"
 	"encoding/base64"
 	"strings"
 	"testing"
@@ -75,3 +76,67 @@ func TestDecodeBase64FileContent(t *testing.T) {
 		})
 	}
 }
+
+// TestDownloadWorkflowContentViaGitValidation ensures that downloadWorkflowContentViaGit
+// rejects dangerous ref/path values before spawning any git subprocess (CWE-88).
+func TestDownloadWorkflowContentViaGitValidation(t *testing.T) {
+	tests := []struct {
+		name        string
+		repo        string
+		path        string
+		ref         string
+		errContains string
+	}{
+		{
+			name:        "path starting with dash is rejected",
+			repo:        "owner/repo",
+			path:        "--output=/tmp/evil",
+			ref:         "abc123",
+			errContains: "refusing git fallback",
+		},
+		{
+			name:        "ref starting with dash is rejected",
+			repo:        "owner/repo",
+			path:        "workflow.md",
+			ref:         "--upload-pack=evil",
+			errContains: "refusing git fallback",
+		},
+		{
+			name:        "path with traversal is rejected",
+			repo:        "owner/repo",
+			path:        "../../../etc/passwd",
+			ref:         "abc123",
+			errContains: "refusing git fallback",
+		},
+		{
+			name:        "ref with dotdot is rejected",
+			repo:        "owner/repo",
+			path:        "workflow.md",
+			ref:         "main..evil",
+			errContains: "refusing git fallback",
+		},
+		{
+			name:        "empty ref is rejected",
+			repo:        "owner/repo",
+			path:        "workflow.md",
+			ref:         "",
+			errContains: "refusing git fallback",
+		},
+		{
+			name:        "empty path is rejected",
+			repo:        "owner/repo",
+			path:        "",
+			ref:         "abc123",
+			errContains: "refusing git fallback",
+		},
+	}
+
+	ctx := context.Background()
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := downloadWorkflowContentViaGit(ctx, tt.repo, tt.path, tt.ref, false)
+			require.Error(t, err, "expected validation error for invalid input")
+			assert.Contains(t, err.Error(), tt.errContains)
+		})
+	}
+}