CVE-2024-1455 (published 2024-03-26T14:15Z)

A vulnerability in the langchain-ai/langchain repository allows for a Billion Laughs Attack, a type of XML External Entity (XXE) exploitation. By nesting multiple layers of entities within an XML document, an attacker can cause the XML parser to consume excessive CPU and memory resources, leading to a denial of service (DoS). 


Weakness information:
cwe_id: CWE-776
cwe_name: Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
description: The product uses XML documents and allows their structure to be defined with a Document Type Definition (DTD), but it does not properly control the number of recursive definitions of entities.
extended_description: If the DTD contains a large number of nested or recursive entities, this can lead to explosive growth of data when parsed, causing a denial of service.
         

Fix information:
repo_url: https://github.com/langchain-ai/langchain
commit_details: repo_url: https://github.com/langchain-ai/langchain
author: Eugene Yurtsev
author_date: 2024-03-25 16:21:52-04:00
msg: core[patch]: Use defusedxml in XMLOutputParser (#19526)

This mitigates a security concern for users still using older versions of libexpat that causes an attacker to compromise the availability of the system if an attacker manages to surface malicious payload to this XMLParser.
repository: repo_url: https://github.com/langchain-ai/langchain
repo_name: langchain-ai/langchain
description: 🦜🔗 Build context-aware reasoning applications
repo_language: Jupyter Notebook
owner: langchain-ai
file_changes: filename: xml.py
change_type: ModificationType.MODIFY
diff: @@ -1,6 +1,7 @@
 import re
-import xml.etree.ElementTree as ET
 from typing import Any, AsyncIterator, Dict, Iterator, List, Optional, Union
+from xml.etree import ElementTree as ET
+from xml.etree.ElementTree import TreeBuilder
 
 from langchain_core.exceptions import OutputParserException
 from langchain_core.messages import BaseMessage
@@ -35,6 +36,10 @@ class XMLOutputParser(BaseTransformOutputParser):
         return XML_FORMAT_INSTRUCTIONS.format(tags=self.tags)
 
     def parse(self, text: str) -> Dict[str, List[Any]]:
+        # Imports are temporarily placed here to avoid issue with caching on CI
+        # likely if you're reading this you can move them to the top of the file
+        from defusedxml import ElementTree as DET  # type: ignore[import]
+
         # Try to find XML string within triple backticks
         match = re.search(r"```(xml)?(.*)```", text, re.DOTALL)
         if match is not None:
@@ -46,18 +51,24 @@ class XMLOutputParser(BaseTransformOutputParser):
 
         text = text.strip()
         try:
-            root = ET.fromstring(text)
+            root = DET.fromstring(text)
             return self._root_to_dict(root)
 
-        except ET.ParseError as e:
+        except (DET.ParseError, DET.EntitiesForbidden) as e:
             msg = f"Failed to parse XML format from completion {text}. Got: {e}"
             raise OutputParserException(msg, llm_output=text) from e
 
     def _transform(
         self, input: Iterator[Union[str, BaseMessage]]
     ) -> Iterator[AddableDict]:
+        # Imports are temporarily placed here to avoid issue with caching on CI
+        # likely if you're reading this you can move them to the top of the file
+        from defusedxml.ElementTree import DefusedXMLParser  # type: ignore[import]
+
+        parser = ET.XMLPullParser(
+            ["start", "end"], _parser=DefusedXMLParser(target=TreeBuilder())
+        )
         xml_start_re = re.compile(r"<[a-zA-Z:_]")
-        parser = ET.XMLPullParser(["start", "end"])
         xml_started = False
         current_path: List[str] = []
         current_path_has_children = False
@@ -83,6 +94,7 @@ class XMLOutputParser(BaseTransformOutputParser):
             parser.feed(buffer)
             buffer = ""
             # yield all events
+
             for event, elem in parser.read_events():
                 if event == "start":
                     # update current path
@@ -105,9 +117,17 @@ class XMLOutputParser(BaseTransformOutputParser):
     async def _atransform(
         self, input: AsyncIterator[Union[str, BaseMessage]]
     ) -> AsyncIterator[AddableDict]:
-        parser = ET.XMLPullParser(["start", "end"])
+        # Imports are temporarily placed here to avoid issue with caching on CI
+        # likely if you're reading this you can move them to the top of the file
+        from defusedxml.ElementTree import DefusedXMLParser  # type: ignore[import]
+
+        _parser = DefusedXMLParser(target=TreeBuilder())
+        parser = ET.XMLPullParser(["start", "end"], _parser=_parser)
+        xml_start_re = re.compile(r"<[a-zA-Z:_]")
+        xml_started = False
         current_path: List[str] = []
         current_path_has_children = False
+        buffer = ""
         async for chunk in input:
             if isinstance(chunk, BaseMessage):
                 # extract text
@@ -115,8 +135,19 @@ class XMLOutputParser(BaseTransformOutputParser):
                 if not isinstance(chunk_content, str):
                     continue
                 chunk = chunk_content
-            # pass chunk to parser
-            parser.feed(chunk)
+            # add chunk to buffer of unprocessed text
+            buffer += chunk
+            # if xml string hasn't started yet, continue to next chunk
+            if not xml_started:
+                if match := xml_start_re.search(buffer):
+                    # if xml string has started, remove all text before it
+                    buffer = buffer[match.start() :]
+                    xml_started = True
+                else:
+                    continue
+            # feed buffer to parser
+            parser.feed(buffer)
+            buffer = ""
             # yield all events
             for event, elem in parser.read_events():
                 if event == "start":
@@ -130,7 +161,10 @@ class XMLOutputParser(BaseTransformOutputParser):
                     if not current_path_has_children:
                         yield nested_element(current_path, elem)
                     # prevent yielding of parent element
-                    current_path_has_children = True
+                    if current_path:
+                        current_path_has_children = True
+                    else:
+                        xml_started = False
         # close parser
         parser.close()
 

programming_language: Python
filename: poetry.lock
change_type: ModificationType.MODIFY
diff: @@ -660,13 +660,13 @@ files = [
 
 [[package]]
 name = "importlib-metadata"
-version = "7.0.2"
+version = "7.1.0"
 description = "Read metadata from Python packages"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "importlib_metadata-7.0.2-py3-none-any.whl", hash = "sha256:f4bc4c0c070c490abf4ce96d715f68e95923320370efb66143df00199bb6c100"},
-    {file = "importlib_metadata-7.0.2.tar.gz", hash = "sha256:198f568f3230878cb1b44fbd7975f87906c22336dba2e4a7f05278c281fbd792"},
+    {file = "importlib_metadata-7.1.0-py3-none-any.whl", hash = "sha256:30962b96c0c223483ed6cc7280e7f0199feb01a0e40cfae4d4450fc6fab1f570"},
+    {file = "importlib_metadata-7.1.0.tar.gz", hash = "sha256:b78938b926ee8d5f020fc4772d487045805a55ddbad2ecf21c6d60938dc7fcd2"},
 ]
 
 [package.dependencies]
@@ -675,17 +675,17 @@ zipp = ">=0.5"
 [package.extras]
 docs = ["furo", "jaraco.packaging (>=9.3)", "jaraco.tidelift (>=1.4)", "rst.linker (>=1.9)", "sphinx (>=3.5)", "sphinx-lint"]
 perf = ["ipython"]
-testing = ["flufl.flake8", "importlib-resources (>=1.3)", "packaging", "pyfakefs", "pytest (>=6)", "pytest-checkdocs (>=2.4)", "pytest-cov", "pytest-enabler (>=2.2)", "pytest-mypy", "pytest-perf (>=0.9.2)", "pytest-ruff (>=0.2.1)"]
+testing = ["flufl.flake8", "importlib-resources (>=1.3)", "jaraco.test (>=5.4)", "packaging", "pyfakefs", "pytest (>=6)", "pytest-checkdocs (>=2.4)", "pytest-cov", "pytest-enabler (>=2.2)", "pytest-mypy", "pytest-perf (>=0.9.2)", "pytest-ruff (>=0.2.1)"]
 
 [[package]]
 name = "importlib-resources"
-version = "6.3.1"
+version = "6.4.0"
 description = "Read resources from Python packages"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "importlib_resources-6.3.1-py3-none-any.whl", hash = "sha256:4811639ca7fa830abdb8e9ca0a104dc6ad13de691d9fe0d3173a71304f068159"},
-    {file = "importlib_resources-6.3.1.tar.gz", hash = "sha256:29a3d16556e330c3c8fb8202118c5ff41241cc34cbfb25989bbad226d99b7995"},
+    {file = "importlib_resources-6.4.0-py3-none-any.whl", hash = "sha256:50d10f043df931902d4194ea07ec57960f66a80449ff867bfe782b4c486ba78c"},
+    {file = "importlib_resources-6.4.0.tar.gz", hash = "sha256:cdb2b453b8046ca4e3798eb1d84f3cce1446a0e8e7b5ef4efb600f19fc398145"},
 ]
 
 [package.dependencies]
@@ -693,7 +693,7 @@ zipp = {version = ">=3.1.0", markers = "python_version < \"3.10\""}
 
 [package.extras]
 docs = ["furo", "jaraco.packaging (>=9.3)", "jaraco.tidelift (>=1.4)", "rst.linker (>=1.9)", "sphinx (<7.2.5)", "sphinx (>=3.5)", "sphinx-lint"]
-testing = ["jaraco.collections", "pytest (>=6)", "pytest-checkdocs (>=2.4)", "pytest-cov", "pytest-enabler (>=2.2)", "pytest-mypy", "pytest-ruff (>=0.2.1)", "zipp (>=3.17)"]
+testing = ["jaraco.test (>=5.4)", "pytest (>=6)", "pytest-checkdocs (>=2.4)", "pytest-cov", "pytest-enabler (>=2.2)", "pytest-mypy", "pytest-ruff (>=0.2.1)", "zipp (>=3.17)"]
 
 [[package]]
 name = "iniconfig"
@@ -1020,13 +1020,13 @@ test = ["ipykernel", "pre-commit", "pytest (<8)", "pytest-cov", "pytest-timeout"
 
 [[package]]
 name = "jupyter-events"
-version = "0.9.1"
+version = "0.10.0"
 description = "Jupyter Event System library"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "jupyter_events-0.9.1-py3-none-any.whl", hash = "sha256:e51f43d2c25c2ddf02d7f7a5045f71fc1d5cb5ad04ef6db20da961c077654b9b"},
-    {file = "jupyter_events-0.9.1.tar.gz", hash = "sha256:a52e86f59eb317ee71ff2d7500c94b963b8a24f0b7a1517e2e653e24258e15c7"},
+    {file = "jupyter_events-0.10.0-py3-none-any.whl", hash = "sha256:4b72130875e59d57716d327ea70d3ebc3af1944d3717e5a498b8a06c6c159960"},
+    {file = "jupyter_events-0.10.0.tar.gz", hash = "sha256:670b8229d3cc882ec782144ed22e0d29e1c2d639263f92ca8383e66682845e22"},
 ]
 
 [package.dependencies]
@@ -1216,13 +1216,13 @@ url = "../text-splitters"
 
 [[package]]
 name = "langsmith"
-version = "0.1.27"
+version = "0.1.31"
 description = "Client library to connect to the LangSmith LLM Tracing and Evaluation Platform."
 optional = false
-python-versions = ">=3.8.1,<4.0"
+python-versions = "<4.0,>=3.8.1"
 files = [
-    {file = "langsmith-0.1.27-py3-none-any.whl", hash = "sha256:d223176952b1525c958189ab1b894f5bd9891ec9177222f7a978aeee4bf1cc95"},
-    {file = "langsmith-0.1.27.tar.gz", hash = "sha256:e0a339d976362051adf3fdbc43fcc7c00bb4615a401321ad7e556bd2dab556c0"},
+    {file = "langsmith-0.1.31-py3-none-any.whl", hash = "sha256:5211a9dc00831db307eb843485a97096484b697b5d2cd1efaac34228e97ca087"},
+    {file = "langsmith-0.1.31.tar.gz", hash = "sha256:efd54ccd44be7fda911bfdc0ead340473df2fdd07345c7252901834d0c4aa37e"},
 ]
 
 [package.dependencies]
@@ -1406,13 +1406,13 @@ test = ["flaky", "ipykernel (>=6.19.3)", "ipython", "ipywidgets", "nbconvert (>=
 
 [[package]]
 name = "nbconvert"
-version = "7.16.2"
+version = "7.16.3"
 description = "Converting Jupyter Notebooks (.ipynb files) to other formats.  Output formats include asciidoc, html, latex, markdown, pdf, py, rst, script.  nbconvert can be used both as a Python library (`import nbconvert`) or as a command line tool (invoked as `jupyter nbconvert ...`)."
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "nbconvert-7.16.2-py3-none-any.whl", hash = "sha256:0c01c23981a8de0220255706822c40b751438e32467d6a686e26be08ba784382"},
-    {file = "nbconvert-7.16.2.tar.gz", hash = "sha256:8310edd41e1c43947e4ecf16614c61469ebc024898eb808cce0999860fc9fb16"},
+    {file = "nbconvert-7.16.3-py3-none-any.whl", hash = "sha256:ddeff14beeeedf3dd0bc506623e41e4507e551736de59df69a91f86700292b3b"},
+    {file = "nbconvert-7.16.3.tar.gz", hash = "sha256:a6733b78ce3d47c3f85e504998495b07e6ea9cf9bf6ec1c98dda63ec6ad19142"},
 ]
 
 [package.dependencies]
@@ -1439,7 +1439,7 @@ docs = ["ipykernel", "ipython", "myst-parser", "nbsphinx (>=0.2.12)", "pydata-sp
 qtpdf = ["nbconvert[qtpng]"]
 qtpng = ["pyqtwebengine (>=5.15)"]
 serve = ["tornado (>=6.1)"]
-test = ["flaky", "ipykernel", "ipywidgets (>=7.5)", "pytest"]
+test = ["flaky", "ipykernel", "ipywidgets (>=7.5)", "pytest (>=7)"]
 webpdf = ["playwright"]
 
 [[package]]
@@ -1997,17 +1997,17 @@ testing = ["coverage (>=6.2)", "flaky (>=3.5.0)", "hypothesis (>=5.7.1)", "mypy
 
 [[package]]
 name = "pytest-mock"
-version = "3.12.0"
+version = "3.14.0"
 description = "Thin-wrapper around the mock package for easier use with pytest"
 optional = false
 python-versions = ">=3.8"
 files = [
-    {file = "pytest-mock-3.12.0.tar.gz", hash = "sha256:31a40f038c22cad32287bb43932054451ff5583ff094bca6f675df2f8bc1a6e9"},
-    {file = "pytest_mock-3.12.0-py3-none-any.whl", hash = "sha256:0972719a7263072da3a21c7f4773069bcc7486027d7e8e1f81d98a47e701bc4f"},
+    {file = "pytest-mock-3.14.0.tar.gz", hash = "sha256:2719255a1efeceadbc056d6bf3df3d1c5015530fb40cf347c0f9afac88410bd0"},
+    {file = "pytest_mock-3.14.0-py3-none-any.whl", hash = "sha256:0b72c38033392a5f4621342fe11e9219ac11ec9d375f8e2a0c164539e0d70f6f"},
 ]
 
 [package.dependencies]
-pytest = ">=5.0"
+pytest = ">=6.2.5"
 
 [package.extras]
 dev = ["pre-commit", "pytest-asyncio", "tox"]
@@ -2966,4 +2966,4 @@ extended-testing = ["jinja2"]
 [metadata]
 lock-version = "2.0"
 python-versions = ">=3.8.1,<4.0"
-content-hash = "ca611429e3dd84ce6dac7ef69d7d9b4da78bf467356946e37016b821e5fe752e"
+content-hash = "a13a0a8454b242106bb681fa74e1f1320a0198f2e07b35d29d985b03a310cf67"

programming_language: Lua
filename: pyproject.toml
change_type: ModificationType.MODIFY
diff: @@ -19,6 +19,7 @@ PyYAML = ">=5.3"
 requests = "^2"
 packaging = "^23.2"
 jinja2 = { version = "^3", optional = true }
+defusedxml = "^0.7"
 
 [tool.poetry.group.lint]
 optional = true

programming_language: Python
filename: test_xml_parser.py
change_type: ModificationType.MODIFY
diff: @@ -1,4 +1,7 @@
 """Test XMLOutputParser"""
+from typing import AsyncIterator
+from xml.etree.ElementTree import ParseError
+
 import pytest
 
 from langchain_core.exceptions import OutputParserException
@@ -40,19 +43,29 @@ More random text
 """,
     ],
 )
-def test_xml_output_parser(result: str) -> None:
+async def test_xml_output_parser(result: str) -> None:
     """Test XMLOutputParser."""
 
     xml_parser = XMLOutputParser()
-
-    xml_result = xml_parser.parse(result)
-    assert DEF_RESULT_EXPECTED == xml_result
+    assert DEF_RESULT_EXPECTED == xml_parser.parse(result)
+    assert DEF_RESULT_EXPECTED == (await xml_parser.aparse(result))
     assert list(xml_parser.transform(iter(result))) == [
         {"foo": [{"bar": [{"baz": None}]}]},
         {"foo": [{"bar": [{"baz": "slim.shady"}]}]},
         {"foo": [{"baz": "tag"}]},
     ]
 
+    async def _as_iter(string: str) -> AsyncIterator[str]:
+        for c in string:
+            yield c
+
+    chunks = [chunk async for chunk in xml_parser.atransform(_as_iter(result))]
+    assert chunks == [
+        {"foo": [{"bar": [{"baz": None}]}]},
+        {"foo": [{"bar": [{"baz": "slim.shady"}]}]},
+        {"foo": [{"baz": "tag"}]},
+    ]
+
 
 @pytest.mark.parametrize("result", ["foo></foo>", "<foo></foo", "foo></foo", "foofoo"])
 def test_xml_output_parser_fail(result: str) -> None:
@@ -63,3 +76,41 @@ def test_xml_output_parser_fail(result: str) -> None:
     with pytest.raises(OutputParserException) as e:
         xml_parser.parse(result)
     assert "Failed to parse" in str(e)
+
+
+MALICIOUS_XML = """<?xml version="1.0"?>
+<!DOCTYPE lolz [<!ENTITY lol "lol"><!ELEMENT lolz (#PCDATA)>
+ <!ENTITY lol1 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
+ <!ENTITY lol2 "&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;">
+ <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">
+ <!ENTITY lol4 "&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;&lol3;">
+ <!ENTITY lol5 "&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;&lol4;">
+ <!ENTITY lol6 "&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;&lol5;">
+ <!ENTITY lol7 "&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;&lol6;">
+ <!ENTITY lol8 "&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;&lol7;">
+ <!ENTITY lol9 "&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;&lol8;">
+]>
+<lolz>&lol9;</lolz>"""
+
+
+async def tests_billion_laughs_attack() -> None:
+    parser = XMLOutputParser()
+    with pytest.raises(OutputParserException):
+        parser.parse(MALICIOUS_XML)
+
+    with pytest.raises(OutputParserException):
+        await parser.aparse(MALICIOUS_XML)
+
+    with pytest.raises(ParseError):
+        # Right now raises undefined entity error
+        assert list(parser.transform(iter(MALICIOUS_XML))) == [
+            {"foo": [{"bar": [{"baz": None}]}]}
+        ]
+
+    async def _as_iter(string: str) -> AsyncIterator[str]:
+        for c in string:
+            yield c
+
+    with pytest.raises(ParseError):
+        chunks = [chunk async for chunk in parser.atransform(_as_iter(MALICIOUS_XML))]
+        assert chunks == [{"foo": [{"bar": [{"baz": None}]}]}]

programming_language: Python