diff --git a/changedetectionio/jinja2_custom/plugins/__init__.py b/changedetectionio/jinja2_custom/plugins/__init__.py
new file mode 100644
index 00000000..2207aa69
--- /dev/null
+++ b/changedetectionio/jinja2_custom/plugins/__init__.py
@@ -0,0 +1,6 @@
+"""
+Jinja2 custom filter plugins for changedetection.io
+"""
+from .regex import regex_replace
+
+__all__ = ['regex_replace']
diff --git a/changedetectionio/jinja2_custom/plugins/regex.py b/changedetectionio/jinja2_custom/plugins/regex.py
new file mode 100644
index 00000000..a5a16a4b
--- /dev/null
+++ b/changedetectionio/jinja2_custom/plugins/regex.py
@@ -0,0 +1,98 @@
+"""
+Regex filter plugin for Jinja2 templates.
+
+Provides regex_replace filter for pattern-based string replacements in templates.
+"""
+import re
+import signal
+from loguru import logger
+
+
+def regex_replace(value: str, pattern: str, replacement: str = '', count: int = 0) -> str:
+    """
+    Replace occurrences of a regex pattern in a string.
+
+    Security: Protected against ReDoS (Regular Expression Denial of Service) attacks:
+    - Limits input value size to prevent excessive processing
+    - Uses timeout mechanism to prevent runaway regex operations
+    - Validates pattern complexity to prevent catastrophic backtracking
+
+    Args:
+        value: The input string to perform replacements on
+        pattern: The regex pattern to search for
+        replacement: The replacement string (default: '')
+        count: Maximum number of replacements (0 = replace all, default: 0)
+
+    Returns:
+        String with replacements applied, or original value on error
+
+    Example:
+        {{ "hello world" | regex_replace("world", "universe") }}
+        {{ diff | regex_replace("<td>([^<]+)</td><td>([^<]+)</td>", "Label1: \\1\\nLabel2: \\2") }}
+
+    Security limits:
+        - Maximum input size: 1MB
+        - Maximum pattern length: 500 characters
+        - Operation timeout: 2 seconds
+        - Dangerous nested quantifier patterns are rejected
+    """
+    # Security limits
+    MAX_INPUT_SIZE = 1024 * 1024 * 10 # 10MB max input size
+    MAX_PATTERN_LENGTH = 500  # Maximum regex pattern length
+    REGEX_TIMEOUT_SECONDS = 10  # Maximum time for regex operation
+
+    # Validate input sizes
+    value_str = str(value)
+    if len(value_str) > MAX_INPUT_SIZE:
+        logger.warning(f"regex_replace: Input too large ({len(value_str)} bytes), truncating")
+        value_str = value_str[:MAX_INPUT_SIZE]
+
+    if len(pattern) > MAX_PATTERN_LENGTH:
+        logger.warning(f"regex_replace: Pattern too long ({len(pattern)} chars), rejecting")
+        return value_str
+
+    # Check for potentially dangerous patterns (basic checks)
+    # Nested quantifiers like (a+)+ can cause catastrophic backtracking
+    dangerous_patterns = [
+        r'\([^)]*\+[^)]*\)\+',  # (x+)+
+        r'\([^)]*\*[^)]*\)\+',  # (x*)+
+        r'\([^)]*\+[^)]*\)\*',  # (x+)*
+        r'\([^)]*\*[^)]*\)\*',  # (x*)*
+    ]
+
+    for dangerous in dangerous_patterns:
+        if re.search(dangerous, pattern):
+            logger.warning(f"regex_replace: Potentially dangerous pattern detected: {pattern}")
+            return value_str
+
+    def timeout_handler(signum, frame):
+        raise TimeoutError("Regex operation timed out")
+
+    try:
+        # Set up timeout for regex operation (Unix-like systems only)
+        # This prevents ReDoS attacks
+        old_handler = None
+        if hasattr(signal, 'SIGALRM'):
+            old_handler = signal.signal(signal.SIGALRM, timeout_handler)
+            signal.alarm(REGEX_TIMEOUT_SECONDS)
+
+        try:
+            result = re.sub(pattern, replacement, value_str, count=count)
+        finally:
+            # Cancel the alarm
+            if hasattr(signal, 'SIGALRM'):
+                signal.alarm(0)
+                if old_handler is not None:
+                    signal.signal(signal.SIGALRM, old_handler)
+
+        return result
+
+    except TimeoutError:
+        logger.error(f"regex_replace: Regex operation timed out - possible ReDoS attack. Pattern: {pattern}")
+        return value_str
+    except re.error as e:
+        logger.warning(f"regex_replace: Invalid regex pattern: {e}")
+        return value_str
+    except Exception as e:
+        logger.error(f"regex_replace: Unexpected error: {e}")
+        return value_str
diff --git a/changedetectionio/jinja2_custom/safe_jinja.py b/changedetectionio/jinja2_custom/safe_jinja.py
index c34c94ba..cf7d710c 100644
--- a/changedetectionio/jinja2_custom/safe_jinja.py
+++ b/changedetectionio/jinja2_custom/safe_jinja.py
@@ -7,14 +7,15 @@ See https://jinja.palletsprojects.com/en/3.1.x/sandbox/#security-considerations
 import jinja2.sandbox
 import typing as t
 import os
+import re
 from .extensions.TimeExtension import TimeExtension
+from .plugins import regex_replace
 
 JINJA2_MAX_RETURN_PAYLOAD_SIZE = 1024 * int(os.getenv("JINJA2_MAX_RETURN_PAYLOAD_SIZE_KB", 1024 * 10))
 
 # Default extensions - can be overridden in create_jinja_env()
 DEFAULT_JINJA2_EXTENSIONS = [TimeExtension]
 
-
 def create_jinja_env(extensions=None, **kwargs) -> jinja2.sandbox.ImmutableSandboxedEnvironment:
     """
     Create a sandboxed Jinja2 environment with our custom extensions and default timezone.
@@ -38,6 +39,9 @@ def create_jinja_env(extensions=None, **kwargs) -> jinja2.sandbox.ImmutableSandb
     default_timezone = os.getenv('TZ', 'UTC').strip()
     jinja2_env.default_timezone = default_timezone
 
+    # Register custom filters
+    jinja2_env.filters['regex_replace'] = regex_replace
+
     return jinja2_env
 
 
diff --git a/changedetectionio/tests/test_jinja2.py b/changedetectionio/tests/test_jinja2.py
index dce38571..e1c97677 100644
--- a/changedetectionio/tests/test_jinja2.py
+++ b/changedetectionio/tests/test_jinja2.py
@@ -169,4 +169,161 @@ def test_default_timezone_subtraction(environment):
 
     finalRender = render("{% now '' - 'minutes=11' %}")
 
-    assert finalRender == "Wed, 09 Dec 2015 23:22:01"
\ No newline at end of file
+    assert finalRender == "Wed, 09 Dec 2015 23:22:01"
+
+def test_regex_replace_basic():
+    """Test basic regex_replace functionality."""
+
+    # Simple word replacement
+    finalRender = render("{{ 'hello world' | regex_replace('world', 'universe') }}")
+    assert finalRender == "hello universe"
+
+def test_regex_replace_with_groups():
+    """Test regex_replace with capture groups (issue #3501 use case)."""
+
+    # Transform HTML table data as described in the issue
+    template = "{{ '<td>thing</td><td>other</td>' | regex_replace('<td>([^<]+)</td><td>([^<]+)</td>', 'ThingLabel: \\\\1\\nOtherLabel: \\\\2') }}"
+    finalRender = render(template)
+    assert "ThingLabel: thing" in finalRender
+    assert "OtherLabel: other" in finalRender
+
+def test_regex_replace_multiple_matches():
+    """Test regex_replace replacing multiple occurrences."""
+
+    finalRender = render("{{ 'foo bar foo baz' | regex_replace('foo', 'qux') }}")
+    assert finalRender == "qux bar qux baz"
+
+def test_regex_replace_count_parameter():
+    """Test regex_replace with count parameter to limit replacements."""
+
+    finalRender = render("{{ 'foo bar foo baz' | regex_replace('foo', 'qux', 1) }}")
+    assert finalRender == "qux bar foo baz"
+
+def test_regex_replace_empty_replacement():
+    """Test regex_replace with empty replacement (removal)."""
+
+    finalRender = render("{{ 'hello world 123' | regex_replace('[0-9]+', '') }}")
+    assert finalRender == "hello world "
+
+def test_regex_replace_no_match():
+    """Test regex_replace when pattern doesn't match."""
+
+    finalRender = render("{{ 'hello world' | regex_replace('xyz', 'abc') }}")
+    assert finalRender == "hello world"
+
+def test_regex_replace_invalid_regex():
+    """Test regex_replace with invalid regex pattern returns original value."""
+
+    # Invalid regex (unmatched parenthesis)
+    finalRender = render("{{ 'hello world' | regex_replace('(invalid', 'replacement') }}")
+    assert finalRender == "hello world"
+
+def test_regex_replace_special_characters():
+    """Test regex_replace with special regex characters."""
+
+    finalRender = render("{{ 'Price: $50.00' | regex_replace('\\\\$([0-9.]+)', 'USD \\\\1') }}")
+    assert finalRender == "Price: USD 50.00"
+
+def test_regex_replace_multiline():
+    """Test regex_replace on multiline text."""
+
+    template = "{{ 'line1\\nline2\\nline3' | regex_replace('^line', 'row') }}"
+    finalRender = render(template)
+    # By default re.sub doesn't use MULTILINE flag, so only first line matches with ^
+    assert finalRender == "row1\nline2\nline3"
+
+def test_regex_replace_with_notification_context():
+    """Test regex_replace with notification diff variable."""
+
+    # Simulate how it would be used in notifications with diff variable
+    from changedetectionio.notification_service import NotificationContextData
+
+    context = NotificationContextData()
+    context['diff'] = '<td>value1</td><td>value2</td>'
+
+    template = "{{ diff | regex_replace('<td>([^<]+)</td>', '\\\\1 ') }}"
+
+    from changedetectionio.jinja2_custom import create_jinja_env
+    from jinja2 import BaseLoader
+
+    jinja2_env = create_jinja_env(loader=BaseLoader)
+    jinja2_env.globals.update(context)
+    finalRender = jinja2_env.from_string(template).render()
+
+    assert "value1 value2 " in finalRender
+
+def test_regex_replace_security_large_input():
+    """Test regex_replace handles large input safely."""
+
+    # Create a large input string (over 1MB)
+    large_input = "x" * (1024 * 1024 + 1000)
+    template = "{{ large_input | regex_replace('x', 'y') }}"
+
+    from changedetectionio.jinja2_custom import create_jinja_env
+    from jinja2 import BaseLoader
+
+    jinja2_env = create_jinja_env(loader=BaseLoader)
+    jinja2_env.globals['large_input'] = large_input
+    finalRender = jinja2_env.from_string(template).render()
+
+    # Should be truncated to 1MB
+    assert len(finalRender) == 1024 * 1024
+
+def test_regex_replace_security_long_pattern():
+    """Test regex_replace rejects very long patterns."""
+
+    # Pattern longer than 500 chars should be rejected
+    long_pattern = "a" * 501
+    finalRender = render("{{ 'test' | regex_replace('" + long_pattern + "', 'replacement') }}")
+
+    # Should return original value when pattern is too long
+    assert finalRender == "test"
+
+def test_regex_replace_security_dangerous_pattern():
+    """Test regex_replace detects and rejects dangerous nested quantifiers."""
+
+    # Patterns that could cause catastrophic backtracking
+    dangerous_patterns = [
+        "(a+)+",
+        "(a*)+",
+        "(a+)*",
+        "(a*)*",
+    ]
+
+    for dangerous in dangerous_patterns:
+        # Create a template with the dangerous pattern
+        # Using single quotes to avoid escaping issues
+        from changedetectionio.jinja2_custom import create_jinja_env
+        from jinja2 import BaseLoader
+
+        jinja2_env = create_jinja_env(loader=BaseLoader)
+        jinja2_env.globals['pattern'] = dangerous
+        template = "{{ 'aaaaaaaaaa' | regex_replace(pattern, 'x') }}"
+        finalRender = jinja2_env.from_string(template).render()
+
+        # Should return original value when dangerous pattern is detected
+        assert finalRender == "aaaaaaaaaa"
+
+def test_regex_replace_security_timeout_protection():
+    """Test that regex_replace has timeout protection (if SIGALRM available)."""
+    import signal
+
+    # Only test on systems that support SIGALRM
+    if not hasattr(signal, 'SIGALRM'):
+        # Skip test on Windows and other systems without SIGALRM
+        return
+
+    # This pattern is known to cause exponential backtracking on certain inputs
+    # but should be caught by our dangerous pattern detector
+    # We're mainly testing that the timeout mechanism works
+
+    from changedetectionio.jinja2_custom import regex_replace
+
+    # Create input that could trigger slow regex
+    test_input = "a" * 50 + "b"
+
+    # This shouldn't take long due to our protections
+    result = regex_replace(test_input, "a+b", "x")
+
+    # Should complete and return a result
+    assert result is not None
\ No newline at end of file