diff --git a/act/runner/command.go b/act/runner/command.go
index 477738c0..5ac20e95 100644
--- a/act/runner/command.go
+++ b/act/runner/command.go
@@ -51,7 +51,7 @@ func (rc *RunContext) commandHandler(ctx context.Context) common.LineHandler {
 			logger.Infof("%s", line)
 			return false
 		}
-		arg = unescapeCommandData(arg)
+		arg = UnescapeCommandData(arg)
 		kvPairs = unescapeKvPairs(kvPairs)
 		switch command {
 		case "set-env":
@@ -151,7 +151,7 @@ func parseKeyValuePairs(kvPairs, separator string) map[string]string {
 	return rtn
 }
 
-func unescapeCommandData(arg string) string {
+func UnescapeCommandData(arg string) string {
 	escapeMap := map[string]string{
 		"%25": "%",
 		"%0D": "\r",
diff --git a/act/runner/logger.go b/act/runner/logger.go
index fbf93732..d364420d 100644
--- a/act/runner/logger.go
+++ b/act/runner/logger.go
@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"slices"
 	"strings"
 	"sync"
 
@@ -166,9 +167,29 @@ func withStepLogger(ctx context.Context, stepNumber int, stepID, stepName, stage
 
 type entryProcessor func(entry *logrus.Entry) *logrus.Entry
 
+func AppendSecretMasker(oldnew []string, v string) []string {
+	ret := oldnew
+
+	for l := range strings.SplitSeq(v, "\n") {
+		tm := strings.TrimSpace(l)
+		// formatted JSON secrets could otherwise mask {,[,],} everywhere
+		if len(tm) > 1 {
+			ret = append(ret, tm, "***")
+		}
+	}
+
+	return ret
+}
+
 // valueMasker applies secrets and ::add-mask:: patterns to every log entry, including
 // raw_output (command/stream) lines; there is no bypass by field.
 func valueMasker(insecureSecrets bool, secrets map[string]string) entryProcessor {
+	var oldnew []string
+	for _, v := range secrets {
+		oldnew = AppendSecretMasker(oldnew, v)
+	}
+	oldnew = slices.Clip(oldnew)
+	defReplacer := strings.NewReplacer(oldnew...)
 	return func(entry *logrus.Entry) *logrus.Entry {
 		if insecureSecrets {
 			return entry
@@ -176,16 +197,16 @@ func valueMasker(insecureSecrets bool, secrets map[string]string) entryProcessor
 
 		masks := Masks(entry.Context)
 
-		for _, v := range secrets {
-			if v != "" {
-				entry.Message = strings.ReplaceAll(entry.Message, v, "***")
-			}
-		}
+		if len(*masks) == 0 {
+			entry.Message = defReplacer.Replace(entry.Message)
+		} else {
+			cmasker := oldnew
 
-		for _, v := range *masks {
-			if v != "" {
-				entry.Message = strings.ReplaceAll(entry.Message, v, "***")
+			for _, v := range *masks {
+				cmasker = AppendSecretMasker(cmasker, v)
 			}
+
+			entry.Message = strings.NewReplacer(cmasker...).Replace(entry.Message)
 		}
 
 		return entry
diff --git a/act/runner/logger_test.go b/act/runner/logger_test.go
new file mode 100644
index 00000000..de3fc9e9
--- /dev/null
+++ b/act/runner/logger_test.go
@@ -0,0 +1,52 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestValueMasker(t *testing.T) {
+	table := []struct {
+		name       string
+		lines      string
+		secrets    map[string]string
+		masks      []string
+		disallowed []string
+	}{
+		{
+			name:  "Multiline Private Key",
+			lines: "cat << EOF > private.key\nPRIVATE_KEY_BEGIN\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\nPRIVATE_KEY_END\nEOF",
+			secrets: map[string]string{
+				"PRIVATE_KEY": "PRIVATE_KEY_BEGIN\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\nPRIVATE_KEY_END",
+			},
+			disallowed: []string{"KEY", "dsdfseffefsefes", "PRIVATE_KEY_END"},
+		},
+		{
+			name:       "Multiline Private Key in masks",
+			lines:      "cat << EOF > private.key\nPRIVATE_KEY_BEGIN\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\nPRIVATE_KEY_END\nEOF",
+			masks:      []string{"PRIVATE_KEY_BEGIN\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\ndsdfseffefsefes\nPRIVATE_KEY_END"},
+			disallowed: []string{"KEY", "dsdfseffefsefes", "PRIVATE_KEY_END"},
+		},
+	}
+	for _, entry := range table {
+		t.Run(entry.name, func(t *testing.T) {
+			ctx := WithMasks(t.Context(), &entry.masks)
+			masker := valueMasker(false, entry.secrets)
+			for line := range strings.SplitSeq(entry.lines, "\n") {
+				lentry := masker(&logrus.Entry{
+					Context: ctx,
+					Message: line,
+				})
+				for _, line := range entry.disallowed {
+					assert.NotContains(t, lentry.Message, line)
+				}
+			}
+		})
+	}
+}
diff --git a/internal/pkg/report/reporter.go b/internal/pkg/report/reporter.go
index 5dbea735..9f0c653f 100644
--- a/internal/pkg/report/reporter.go
+++ b/internal/pkg/report/reporter.go
@@ -13,6 +13,7 @@ import (
 	"sync/atomic"
 	"time"
 
+	"gitea.com/gitea/runner/act/runner"
 	"gitea.com/gitea/runner/internal/pkg/client"
 	"gitea.com/gitea/runner/internal/pkg/config"
 	"gitea.com/gitea/runner/internal/pkg/metrics"
@@ -73,13 +74,13 @@ type Reporter struct {
 func NewReporter(ctx context.Context, cancel context.CancelFunc, client client.Client, task *runnerv1.Task, cfg *config.Config) *Reporter {
 	var oldnew []string
 	if v := task.Context.Fields["token"].GetStringValue(); v != "" {
-		oldnew = append(oldnew, v, "***")
+		oldnew = runner.AppendSecretMasker(oldnew, v)
 	}
 	if v := task.Context.Fields["gitea_runtime_token"].GetStringValue(); v != "" {
-		oldnew = append(oldnew, v, "***")
+		oldnew = runner.AppendSecretMasker(oldnew, v)
 	}
 	for _, v := range task.Secrets {
-		oldnew = append(oldnew, v, "***")
+		oldnew = runner.AppendSecretMasker(oldnew, v)
 	}
 
 	rv := &Reporter{
@@ -689,7 +690,7 @@ func (r *Reporter) parseLogRow(entry *log.Entry) *runnerv1.LogRow {
 
 	matches := cmdRegex.FindStringSubmatch(content)
 	if matches != nil {
-		if output := r.handleCommand(content, matches[1], matches[3]); output != nil {
+		if output := r.handleCommand(content, matches[1], runner.UnescapeCommandData(matches[3])); output != nil {
 			content = *output
 		} else {
 			return nil
@@ -705,6 +706,6 @@ func (r *Reporter) parseLogRow(entry *log.Entry) *runnerv1.LogRow {
 }
 
 func (r *Reporter) addMask(msg string) {
-	r.oldnew = append(r.oldnew, msg, "***")
+	r.oldnew = runner.AppendSecretMasker(r.oldnew, msg)
 	r.logReplacer = strings.NewReplacer(r.oldnew...)
 }
diff --git a/internal/pkg/report/reporter_test.go b/internal/pkg/report/reporter_test.go
index 3d76ea1f..4c25dfa3 100644
--- a/internal/pkg/report/reporter_test.go
+++ b/internal/pkg/report/reporter_test.go
@@ -50,6 +50,19 @@ func TestReporter_parseLogRow(t *testing.T) {
 				"foo *** bar",
 			},
 		},
+		{
+			"Add-mask-multiline", false,
+			[]string{
+				"foo mysecret bar",
+				"::add-mask::LINE1%0ALINE2",
+				"foo LINE1 bar",
+			},
+			[]string{
+				"foo mysecret bar",
+				"<nil>",
+				"foo *** bar",
+			},
+		},
 		{
 			"Debug enabled", true,
 			[]string{