CVE-2021-23423 (published 2021-08-16T08:15Z)

This affects the package bikeshed before 3.0.0. This can occur when an untrusted source file containing include, include-code or include-raw block is processed. The contents of arbitrary files could be disclosed in the HTML output.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:P/I:N/A:N)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N)

Weakness information:
cwe_id: CWE-22
cwe_name: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
description: The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
extended_description: 
            Many file operations are intended to take place within a restricted directory. By using special elements such as ".." and "/" separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the "../" sequence, which in most modern operating systems is interpreted as the parent directory of the current location. This is referred to as relative path traversal. Path traversal also covers the use of absolute pathnames such as "/usr/local/bin" to access unexpected files. This is referred to as absolute path traversal.
         
         

Fix information:
repo_url: https://github.com/tabatkins/bikeshed
commit_details: repo_url: https://github.com/tabatkins/bikeshed
author: Tab Atkins-Bittner
author_date: 2021-08-06 17:41:38-07:00
msg: Prevent escaping the source doc's folder, or running arbitrary code, without explicit opt-in at the command-line.
repository: repo_url: https://github.com/tabatkins/bikeshed
repo_name: speced/bikeshed
description: :bike: A preprocessor for anyone writing specifications that converts source files into actual specs.
repo_language: HTML
owner: tabatkins
file_changes: filename: InputSource.py
change_type: ModificationType.MODIFY
diff: @@ -13,6 +13,7 @@ import attr
 import requests
 import tenacity
 
+from . import config
 from .Line import Line
 
 
@@ -38,17 +39,17 @@ class InputSource:
     manager for temporarily switching to the directory of a file InputSource.
     """
 
-    def __new__(cls, sourceName: str):
+    def __new__(cls, sourceName: str, **kwargs):
         """Dispatches to the right subclass."""
         if cls != InputSource:
             # Only take control of calls to InputSource(...) itself.
             return super().__new__(cls)
 
         if sourceName == "-":
-            return StdinInputSource(sourceName)
+            return StdinInputSource(sourceName, **kwargs)
         if sourceName.startswith("https:"):
-            return UrlInputSource(sourceName)
-        return FileInputSource(sourceName)
+            return UrlInputSource(sourceName, **kwargs)
+        return FileInputSource(sourceName, **kwargs)
 
     @abstractmethod
     def __str__(self) -> str:
@@ -157,11 +158,17 @@ class UrlInputSource(InputSource):
 
 
 class FileInputSource(InputSource):
-    def __init__(self, sourceName: str):
+    def __init__(self, sourceName: str, *, chroot: bool, chrootPath: Optional[str] = None):
         self.sourceName = sourceName
+        self.chrootPath = chrootPath
         self.type = "file"
         self.content = None
 
+        if chroot and self.chrootPath is None:
+            self.chrootPath = self.directory()
+        if self.chrootPath is not None:
+            self.sourceName = config.chrootPath(self.chrootPath, self.sourceName)
+
     def __str__(self) -> str:
         return self.sourceName
 
@@ -179,7 +186,7 @@ class FileInputSource(InputSource):
         return os.path.dirname(os.path.abspath(self.sourceName))
 
     def relative(self, relativePath) -> FileInputSource:
-        return FileInputSource(os.path.join(self.directory(), relativePath))
+        return FileInputSource(os.path.join(self.directory(), relativePath), chroot=False, chrootPath=self.chrootPath)
 
     def cheaplyExists(self, relativePath) -> bool:
         return os.access(self.relative(relativePath).sourceName, os.R_OK)

programming_language: Python
filename: Spec.py
change_type: ModificationType.MODIFY
diff: @@ -58,7 +58,7 @@ class Spec:
                 "No input file specified, and no *.bs or *.src.html files found in current directory.\nPlease specify an input file, or use - to pipe from STDIN."
             )
             return
-        self.inputSource = InputSource(inputFilename)
+        self.inputSource = InputSource(inputFilename, chroot=constants.chroot)
         self.transitiveDependencies = set()
         self.debug = debug
         self.token = token

programming_language: Python
filename: cli.py
change_type: ModificationType.MODIFY
diff: @@ -75,6 +75,18 @@ def main():
         choices=["nothing", "fatal", "link-error", "warning", "everything"],
         help="Determines what sorts of errors cause Bikeshed to die (quit immediately with an error status code). Default is 'fatal'; the -f flag is a shorthand for 'nothing'",
     )
+    argparser.add_argument(
+        "--allow-nonlocal-files",
+        dest="allowNonlocalFiles",
+        action="store_true",
+        help="Allows Bikeshed to see/include files from folders higher than the one your source document is in."
+    )
+    argparser.add_argument(
+        "--allow-execute",
+        dest="allowExecute",
+        action="store_true",
+        help="Allow some features to execute arbitrary code from outside the Bikeshed codebase."
+    )
 
     subparsers = argparser.add_subparsers(title="Subcommands", dest="subparserName")
 
@@ -444,6 +456,8 @@ def main():
             constants.printMode = "console"
     else:
         constants.printMode = options.printMode
+    constants.chroot = not options.allowNonlocalFiles
+    constants.executeCode = options.allowExecute
 
     update.fixupDataFiles()
     if options.subparserName == "update":

programming_language: Python
filename: main.py
change_type: ModificationType.MODIFY
diff: @@ -4,6 +4,9 @@ import re
 
 import lxml
 
+from .. import constants
+from .. import messages
+
 
 def englishFromList(items, conjunction="or"):
     # Format a list of strings into an English list.
@@ -168,7 +171,19 @@ def flatten(arr):
 
 def scriptPath(*pathSegs):
     startPath = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
-    return os.path.join(startPath, *pathSegs)
+    path = os.path.join(startPath, *pathSegs)
+    return path
+
+
+def chrootPath(chrootPath, path):
+    chrootPath = os.path.abspath(chrootPath)
+    path = os.path.abspath(path)
+    if not path.startswith(chrootPath):
+        messages.die(f"Attempted to access a file ({path}) outside the source document's directory ({chrootPath}). See --allow-nonlocal-files.")
+        raise Exception()
+    else:
+        return path
+
 
 
 def doEvery(s, action, lastTime=None):

programming_language: Python
filename: retrieve.py
change_type: ModificationType.MODIFY
diff: @@ -63,7 +63,7 @@ defaultRequester = DataFileRequester(
 )
 
 
-def retrieveBoilerplateFile(doc, name, group=None, status=None, error=True):
+def retrieveBoilerplateFile(doc, name, group=None, status=None, error=True, allowLocal=True):
     # Looks in three or four locations, in order:
     # the folder the spec source is in, the group's boilerplate folder, the megagroup's boilerplate folder, and the generic boilerplate folder.
     # In each location, it first looks for the file specialized on status, and then for the generic file.
@@ -77,7 +77,7 @@ def retrieveBoilerplateFile(doc, name, group=None, status=None, error=True):
             status = doc.md.rawStatus
     megaGroup, status = splitStatus(status)
 
-    searchLocally = doc.md.localBoilerplate[name]
+    searchLocally = allowLocal and doc.md.localBoilerplate[name]
 
     def boilerplatePath(*segs):
         return scriptPath("boilerplate", *segs)
@@ -101,13 +101,13 @@ def retrieveBoilerplateFile(doc, name, group=None, status=None, error=True):
                 # We should remove this after giving specs time to react to the warning:
                 sources.append(doc.inputSource.relative(f))
     if group:
-        sources.append(InputSource(boilerplatePath(group, statusFile)))
-        sources.append(InputSource(boilerplatePath(group, genericFile)))
+        sources.append(InputSource(boilerplatePath(group, statusFile), chroot=False))
+        sources.append(InputSource(boilerplatePath(group, genericFile), chroot=False))
     if megaGroup:
-        sources.append(InputSource(boilerplatePath(megaGroup, statusFile)))
-        sources.append(InputSource(boilerplatePath(megaGroup, genericFile)))
-    sources.append(InputSource(boilerplatePath(statusFile)))
-    sources.append(InputSource(boilerplatePath(genericFile)))
+        sources.append(InputSource(boilerplatePath(megaGroup, statusFile), chroot=False))
+        sources.append(InputSource(boilerplatePath(megaGroup, genericFile), chroot=False))
+    sources.append(InputSource(boilerplatePath(statusFile), chroot=False))
+    sources.append(InputSource(boilerplatePath(genericFile), chroot=False))
 
     # Watch all the possible sources, not just the one that got used, because if
     # an earlier one appears, we want to rebuild.

programming_language: Python
filename: constants.py
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,8 @@ refStatus = StringEnum("current", "snapshot")
 biblioDisplay = StringEnum("index", "inline")
 specClass = None
 testAnnotationURL = "https://test.csswg.org/harness/annotate.js"
+chroot = True
+executeCode = False
 
 
 def errorLevelAt(target):

programming_language: Python
filename: extensions.py
change_type: ModificationType.MODIFY
diff: @@ -1,8 +1,9 @@
 from . import config
+from . import constants
 from .h import *  # noqa: F401
 from .messages import *  # noqa: F401
 
 
 def load(doc):
-    code = config.retrieveBoilerplateFile(doc, "bs-extensions")
+    code = config.retrieveBoilerplateFile(doc, "bs-extensions", allowLocal=constants.executeCode)
     exec(code, globals())

programming_language: Python
filename: __init__.py
change_type: ModificationType.MODIFY
diff: @@ -1,11 +1,15 @@
 from subprocess import PIPE, Popen
 
+from .. import constants
 from ..h import *
 from ..messages import *
 
 
 def processTags(doc):
     for el in findAll("[data-span-tag]", doc):
+        if not constants.executeCode:
+            die("Found an inline code tag, but arbitrary code execution isn't allowed. See the --allow-execute flag.")
+            return
         tag = el.get("data-span-tag")
         if tag not in doc.md.inlineTagCommands:
             die("Unknown inline tag '{0}' found:\n  {1}", tag, outerHTML(el), el=el)

programming_language: Python