diff --git a/.gitignore b/.gitignore
index 59d621d..c324044 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,3 +24,4 @@ java/.settings/
 .tox/
 .eggs/
 *.egg-info/
+/.venv/
diff --git a/README.md b/README.md
index a28e9cf..f4ca834 100644
--- a/README.md
+++ b/README.md
@@ -7,5 +7,23 @@ This project includes common logic for testing Confluent's Docker images.
 For more information, see: https://docs.confluent.io/platform/current/installation/docker/development.html#docker-utility-belt-dub
 
 
+## Extending the Java CLASSPATH
+
+The `cub` utility now supports extending the Java CLASSPATH at runtime via environment variables:
+
+- `CUB_CLASSPATH` (existing): overrides the entire base classpath when set. Keep quotes if you pass it as a single value.
+- `CUB_CLASSPATH_DIRS` (new): append one or more directories to the base classpath.
+  - Accepts multiple entries separated by `:`, `;` or `,`.
+  - Each directory is normalized to include all jars within it (a trailing `/*` is added if missing).
+  - The final CLASSPATH is kept quoted to avoid shell expansion issues.
+  - The final classpath separator is always `:` (Linux/JVM convention in Confluent images).
+- `CUB_EXTRA_CLASSPATH` (legacy fallback): used only if `CUB_CLASSPATH_DIRS` is not set.
+
+Examples:
+- Linux: set `CUB_CLASSPATH_DIRS=/opt/libs:/opt/plugins,/usr/share/java/custom`
+- Windows host (executing inside Linux containers): set `CUB_CLASSPATH_DIRS=C:\\libs;C:\\plugins` — entries are parsed but the resulting CLASSPATH uses `:` between segments.
+
+If neither `CUB_CLASSPATH_DIRS` nor `CUB_EXTRA_CLASSPATH` is provided, the default base classpath is used.
+
 ## License
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fconfluentinc%2Fconfluent-docker-utils.svg?type=large)](https://app.fossa.com/projects/git%2Bgithub.com%2Fconfluentinc%2Fconfluent-docker-utils?ref=badge_large)
diff --git a/confluent/docker_utils/cub.py b/confluent/docker_utils/cub.py
index 05d9a32..c48cbe9 100755
--- a/confluent/docker_utils/cub.py
+++ b/confluent/docker_utils/cub.py
@@ -46,7 +46,54 @@
 import time
 from requests.auth import HTTPBasicAuth
 
-CLASSPATH = os.environ.get("CUB_CLASSPATH", '"/usr/share/java/cp-base/*:/usr/share/java/cp-base-new/*"')
+# Build CLASSPATH with optional extra directories from env var CUB_CLASSPATH_DIRS (or fallback CUB_EXTRA_CLASSPATH)
+# - Accepts one or more directories separated by ':' ';' or ','
+# - For each directory, if no wildcard/jar is provided, appends '/*' to include all jars within
+# - Uses ':' as final classpath separator (Linux/JVM convention)
+DEFAULT_BASE_CLASSPATH = '"/usr/share/java/cp-base/*:/usr/share/java/cp-base-new/*"'
+
+def _strip_outer_quotes(s):
+    s = s.strip()
+    if (s.startswith('"') and s.endswith('"')) or (s.startswith("'") and s.endswith("'")):
+        return s[1:-1]
+    return s
+
+def _normalize_extra_classpath(extra_value):
+    if not extra_value:
+        return []
+    parts = re.split(r'[;:,]', extra_value)
+    normalized = []
+    for p in parts:
+        p = p.strip()
+        if not p:
+            continue
+        # If user already provided wildcard or a specific jar/file, keep as is
+        if '*' in p or p.endswith('.jar') or p.endswith('/'):
+            # If it ends with a path separator but no wildcard, append '*'
+            if p.endswith('/') and '*' not in p and not p.endswith('/*'):
+                p = p.rstrip('/') + '/*'
+            normalized.append(p)
+        else:
+            # Append wildcard to include jars under the directory
+            normalized.append(p.rstrip('/') + '/*')
+    return normalized
+
+def _build_classpath():
+    base = os.environ.get("CUB_CLASSPATH", DEFAULT_BASE_CLASSPATH)
+    extra = os.environ.get("CUB_CLASSPATH_DIRS") or os.environ.get("CUB_EXTRA_CLASSPATH") or ""
+
+    base_unquoted = _strip_outer_quotes(base)
+    extras = _normalize_extra_classpath(extra)
+
+    if not extras:
+        # Keep original quoting
+        return base if base.strip() else DEFAULT_BASE_CLASSPATH
+
+    sep = ":"  # Always use JVM/Linux classpath separator
+    full = sep.join([p for p in [base_unquoted] + extras if p])
+    return f'"{full}"'
+
+CLASSPATH = _build_classpath()
 LOG4J_FILE_NAME = "log4j.properties"
 DEFAULT_LOG4J_FILE = f"/etc/cp-base-new/{LOG4J_FILE_NAME}"
 LOG4J2_FILE_NAME = "log4j2.yaml"
diff --git a/docs/CHANGELOG.rst b/docs/CHANGELOG.rst
index ef76782..85d0d7f 100644
--- a/docs/CHANGELOG.rst
+++ b/docs/CHANGELOG.rst
@@ -1,3 +1,10 @@
+Unreleased
+--------------------------------------------------------------------------------
+
+* Add `CUB_CLASSPATH_DIRS` environment variable to append one or more directories to the Java CLASSPATH (fallback to `CUB_EXTRA_CLASSPATH`).
+  Accepts `:`, `;` or `,` separators and normalizes each directory to include `/*` when missing.
+
+
 Version 0.0.35
 --------------------------------------------------------------------------------
 
diff --git a/test/test_classpath.py b/test/test_classpath.py
new file mode 100644
index 0000000..112ea96
--- /dev/null
+++ b/test/test_classpath.py
@@ -0,0 +1,45 @@
+import os
+import sys
+import importlib
+from mock import patch
+
+
+def _load_cub_with_env(env):
+    with patch.dict('os.environ', env, clear=True):
+        # Ensure a fresh import to recompute CLASSPATH
+        if 'confluent.docker_utils.cub' in sys.modules:
+            del sys.modules['confluent.docker_utils.cub']
+        mod = importlib.import_module('confluent.docker_utils.cub')
+        return mod
+
+
+def test_classpath_default_kept_when_no_extra():
+    cub = _load_cub_with_env({})
+    assert cub.CLASSPATH == cub.DEFAULT_BASE_CLASSPATH
+
+
+def test_classpath_with_single_dir_via_CUB_CLASSPATH_DIRS():
+    cub = _load_cub_with_env({'CUB_CLASSPATH_DIRS': '/opt/libs'})
+    base_unquoted = cub.DEFAULT_BASE_CLASSPATH[1:-1]
+    expected = '"' + base_unquoted + ':' + '/opt/libs/*' + '"'
+    assert cub.CLASSPATH == expected
+
+
+def test_classpath_with_multiple_dirs_and_delimiters():
+    cub = _load_cub_with_env({'CUB_CLASSPATH_DIRS': '/opt/a, /opt/b;/opt/c: /opt/d/*'})
+    base_unquoted = cub.DEFAULT_BASE_CLASSPATH[1:-1]
+    extras = ['/opt/a/*', '/opt/b/*', '/opt/c/*', '/opt/d/*']
+    expected = '"' + ':'.join([base_unquoted] + extras) + '"'
+    assert cub.CLASSPATH == expected
+
+
+def test_classpath_with_fallback_CUB_EXTRA_CLASSPATH():
+    cub = _load_cub_with_env({'CUB_EXTRA_CLASSPATH': '/ext/libs/'})
+    base_unquoted = cub.DEFAULT_BASE_CLASSPATH[1:-1]
+    expected = '"' + base_unquoted + ':' + '/ext/libs/*' + '"'
+    assert cub.CLASSPATH == expected
+
+
+def test_classpath_respects_explicit_CUB_CLASSPATH_when_no_extra():
+    cub = _load_cub_with_env({'CUB_CLASSPATH': '"/custom/base1/*:/custom/base2/*"'})
+    assert cub.CLASSPATH == '"/custom/base1/*:/custom/base2/*"'