From 5fa54d8b4a257b7195f53c4a336239729d779553 Mon Sep 17 00:00:00 2001
From: Jimmy Liu Jia <1365121844@qq.com>
Date: Sat, 17 Oct 2026 00:38:37 +0800
Subject: [PATCH] Escape conditional formatting formulas in worksheet XML

---
 .../ConditionalFormattingExpressionRule.java      |  2 +-
 .../dhatim/fastexcel/PoiCompatibilityTest.java    | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/fastexcel-writer/src/main/java/org/dhatim/fastexcel/ConditionalFormattingExpressionRule.java b/fastexcel-writer/src/main/java/org/dhatim/fastexcel/ConditionalFormattingExpressionRule.java
index 52368781..13c6cd1e 100644
--- a/fastexcel-writer/src/main/java/org/dhatim/fastexcel/ConditionalFormattingExpressionRule.java
+++ b/fastexcel-writer/src/main/java/org/dhatim/fastexcel/ConditionalFormattingExpressionRule.java
@@ -30,7 +30,7 @@ public ConditionalFormattingExpressionRule(String expression, boolean stopIfTrue
     public void write(Writer w) throws IOException {
         w
             .append("<cfRule type=\"").append(TYPE).append("\" priority=\"").append(priority).append("\" stopIfTrue=\"").append(stopIfTrue ? "1" : "0").append("\" dxfId=\"").append(dxfId).append("\">")
-            .append("<formula>").append(expression).append("</formula>")
+            .append("<formula>").appendEscaped(expression).append("</formula>")
             .append("</cfRule>");
     }
 }
diff --git a/fastexcel-writer/src/test/java/org/dhatim/fastexcel/PoiCompatibilityTest.java b/fastexcel-writer/src/test/java/org/dhatim/fastexcel/PoiCompatibilityTest.java
index 67b3debf..91339f48 100644
--- a/fastexcel-writer/src/test/java/org/dhatim/fastexcel/PoiCompatibilityTest.java
+++ b/fastexcel-writer/src/test/java/org/dhatim/fastexcel/PoiCompatibilityTest.java
@@ -809,6 +809,21 @@ void hasValidCellConditionalFormatting() throws Exception {
         assertTrue(cellRange.formatAsString().equals("A1"));
     }
 
+    @Test
+    void conditionalFormattingExpressionIsEscaped() throws Exception {
+        String formula = "IF(A1<5,A1&\"x\",\"\")";
+        byte[] data = writeWorkbook(wb -> {
+            Worksheet ws = wb.newWorksheet("Worksheet 1");
+            ws.style(0, 0).fillColor("FF8800").set(new ConditionalFormattingExpressionRule(formula, true));
+        });
+
+        try (XSSFWorkbook workbook = new XSSFWorkbook(new ByteArrayInputStream(data))) {
+            XSSFConditionalFormattingRule rule = workbook.getSheetAt(0)
+                    .getSheetConditionalFormatting().getConditionalFormattingAt(0).getRule(0);
+            assertEquals(formula, rule.getFormula1());
+        }
+    }
+
     @Test
     void hasValidRangeConditionalFormatting() throws Exception {
         byte[] data = writeWorkbook(wb -> {