CVE-2019-19010 (published 2019-11-16T01:15Z)

Eval injection in the Math plugin of Limnoria (before 2019.11.09) and Supybot (through 2018-05-09) allows remote unprivileged attackers to disclose information or possibly have unspecified other impact via the calc and icalc IRC commands.

Severity: HIGH
CVSS v2 base score: 7.5 (AV:N/AC:L/Au:N/C:P/I:P/A:P)
CVSS v3 base score: 9.8, CRITICAL (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)

Weakness information:
cwe_id: CWE-94
cwe_name: Improper Control of Generation of Code ('Code Injection')
description: The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
extended_description: 
            When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. Such an alteration could lead to arbitrary code execution.
            Injection problems encompass a wide variety of issues -- all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features which classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common -- i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.
         
         

Fix information:
repo_url: https://github.com/ProgVal/Limnoria
commit_details: repo_url: https://github.com/ProgVal/Limnoria
author: Valentin Lorentz
author_date: 2019-11-09 15:24:37+01:00
msg: Math: Rewrite calc functions with a proper evaluator.

Instead of hacking around eval(), which everyone knows is a bad idea
even with prior expression sanitizing.
repository: repo_url: https://github.com/ProgVal/Limnoria
repo_name: progval/Limnoria
description: A robust, full-featured, and user/programmer-friendly Python IRC bot, with many existing plugins.
repo_language: Python
owner: ProgVal
file_changes: filename: evaluator.py
change_type: ModificationType.ADD
diff: @@ -0,0 +1,169 @@
+###
+# Copyright (c) 2019, Valentin Lorentz
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+#   * Redistributions of source code must retain the above copyright notice,
+#     this list of conditions, and the following disclaimer.
+#   * Redistributions in binary form must reproduce the above copyright notice,
+#     this list of conditions, and the following disclaimer in the
+#     documentation and/or other materials provided with the distribution.
+#   * Neither the name of the author of this software nor the name of
+#     contributors to this software may be used to endorse or promote products
+#     derived from this software without specific prior written consent.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+###
+
+import ast
+import math
+import cmath
+import operator
+
+class InvalidNode(Exception):
+    pass
+
+def filter_module(module, safe_names):
+    return dict([
+        (name, getattr(module, name))
+        for name in safe_names
+        if hasattr(module, name)
+    ])
+
+UNARY_OPS = {
+    ast.UAdd: lambda x: x,
+    ast.USub: lambda x: -x,
+}
+
+BIN_OPS = {
+    ast.Add: operator.add,
+    ast.Sub: operator.sub,
+    ast.Mult: operator.mul,
+    ast.Div: operator.truediv,
+    ast.Pow: operator.pow,
+    ast.BitXor: operator.xor,
+    ast.BitOr: operator.or_,
+    ast.BitAnd: operator.and_,
+}
+
+MATH_CONSTANTS = 'e inf nan pi tau'.split()
+SAFE_MATH_FUNCTIONS = (
+    'acos acosh asin asinh atan atan2 atanh copysign cos cosh degrees erf '
+    'erfc exp expm1 fabs fmod frexp fsum gamma hypot ldexp lgamma log log10 '
+    'log1p log2 modf pow radians remainder sin sinh tan tanh'
+).split()
+SAFE_CMATH_FUNCTIONS = (
+    'acos acosh asin asinh atan atanh cos cosh exp inf infj log log10 '
+    'nanj phase polar rect sin sinh tan tanh tau'
+).split()
+
+SAFE_ENV = filter_module(math, MATH_CONSTANTS + SAFE_MATH_FUNCTIONS)
+SAFE_ENV.update(filter_module(cmath, SAFE_CMATH_FUNCTIONS))
+
+def _sqrt(x):
+    if isinstance(x, complex) or x < 0:
+        return cmath.sqrt(x)
+    else:
+        return math.sqrt(x)
+
+def _cbrt(x):
+    return math.pow(x, 1.0/3)
+
+def _factorial(x):
+    if x<=10000:
+        return float(math.factorial(x))
+    else:
+        raise Exception('factorial argument too large')
+
+SAFE_ENV.update({
+    'i': 1j,
+    'abs': abs,
+    'max': max,
+    'min': min,
+    'round': lambda x, y=0: round(x, int(y)),
+    'factorial': _factorial,
+    'sqrt': _sqrt,
+    'cbrt': _cbrt,
+    'ceil': lambda x: float(math.ceil(x)),
+    'floor': lambda x: float(math.floor(x)),
+})
+
+UNSAFE_ENV = SAFE_ENV.copy()
+# Add functions that return integers
+UNSAFE_ENV.update(filter_module(math, 'ceil floor factorial gcd'.split()))
+
+
+# It would be nice if ast.literal_eval used a visitor so we could subclass
+# to extend it, but it doesn't, so let's reimplement it entirely.
+class SafeEvalVisitor(ast.NodeVisitor):
+    def __init__(self, allow_ints):
+        self._allow_ints = allow_ints
+        self._env = UNSAFE_ENV if allow_ints else SAFE_ENV
+
+    def _convert_num(self, x):
+        """Converts numbers to complex if ints are not allowed."""
+        if self._allow_ints:
+            return x
+        else:
+            x = complex(x)
+            if x.imag == 0:
+                x = x.real
+                # Need to use string-formatting here instead of str() because
+                # use of str() on large numbers loses information:
+                # str(float(33333333333333)) => '3.33333333333e+13'
+                # float('3.33333333333e+13') => 33333333333300.0
+                return float('%.16f' % x)
+            else:
+                return x
+
+    def visit_Expression(self, node):
+        return self.visit(node.body)
+
+    def visit_Num(self, node):
+        return self._convert_num(node.n)
+
+    def visit_Name(self, node):
+        id_ = node.id.lower()
+        if id_ in self._env:
+            return self._env[id_]
+        else:
+            raise NameError(node.id)
+
+    def visit_Call(self, node):
+        func = self.visit(node.func)
+        args = map(self.visit, node.args)
+        # TODO: keywords?
+        return func(*args)
+
+    def visit_UnaryOp(self, node):
+        op = UNARY_OPS.get(node.op.__class__)
+        if op:
+            return op(self.visit(node.operand))
+        else:
+            raise InvalidNode('illegal operator %s' % node.op.__class__.__name__)
+
+    def visit_BinOp(self, node):
+        op = BIN_OPS.get(node.op.__class__)
+        if op:
+            return op(self.visit(node.left), self.visit(node.right))
+        else:
+            raise InvalidNode('illegal operator %s' % node.op.__class__.__name__)
+
+    def generic_visit(self, node):
+        raise InvalidNode('illegal construct %s' % node.__class__.__name__)
+
+def safe_eval(text, allow_ints):
+    node = ast.parse(text, mode='eval')
+    return SafeEvalVisitor(allow_ints).visit(node)

programming_language: Python
filename: plugin.py
change_type: ModificationType.MODIFY
diff: @@ -44,6 +44,7 @@ from supybot.i18n import PluginInternationalization, internationalizeDocstring
 _ = PluginInternationalization('Math')
 
 from .local import convertcore
+from .evaluator import safe_eval, InvalidNode, SAFE_ENV
 
 baseArg = ('int', 'base', lambda i: i <= 36)
 
@@ -97,36 +98,6 @@ class Math(callbacks.Plugin):
             return str(number)
         return self._convertDecimalToBase(number, toBase)
 
-    _mathEnv = {'__builtins__': types.ModuleType('__builtins__'), 'i': 1j}
-    _mathEnv.update(math.__dict__)
-    _mathEnv.update(cmath.__dict__)
-    def _sqrt(x):
-        if isinstance(x, complex) or x < 0:
-            return cmath.sqrt(x)
-        else:
-            return math.sqrt(x)
-    def _cbrt(x):
-        return math.pow(x, 1.0/3)
-    def _factorial(x):
-        if x<=10000:
-            return float(math.factorial(x))
-        else:
-            raise Exception('factorial argument too large')
-    _mathEnv['sqrt'] = _sqrt
-    _mathEnv['cbrt'] = _cbrt
-    _mathEnv['abs'] = abs
-    _mathEnv['max'] = max
-    _mathEnv['min'] = min
-    _mathEnv['round'] = lambda x, y=0: round(x, int(y))
-    _mathSafeEnv = dict([(x,y) for x,y in _mathEnv.items()])
-    _mathSafeEnv['factorial'] = _factorial
-    _mathRe = re.compile(r'((?:(?<![A-Fa-f\d)])-)?'
-                         r'(?:0x[A-Fa-f\d]+|'
-                         r'0[0-7]+|'
-                         r'\d+\.\d+|'
-                         r'\.\d+|'
-                         r'\d+\.|'
-                         r'\d+))')
     def _floatToString(self, x):
         if -1e-10 < x < 1e-10:
             return '0'
@@ -157,17 +128,6 @@ class Math(callbacks.Plugin):
         else:
             return '%s%s' % (realS, imagS)
 
-    _calc_match_forbidden_chars = re.compile('[_\[\]]')
-    _calc_remover = utils.str.MultipleRemover('_[] \t')
-    ###
-    # So this is how the 'calc' command works:
-    # First, we make a nice little safe environment for evaluation; basically,
-    # the names in the 'math' and 'cmath' modules.  Then, we remove the ability
-    # of a random user to get ints evaluated: this means we have to turn all
-    # int literals (even octal numbers and hexadecimal numbers) into floats.
-    # Then we delete all square brackets, underscores, and whitespace, so no
-    # one can do list comprehensions or call __...__ functions.
-    ###
     @internationalizeDocstring
     def calc(self, irc, msg, args, text):
         """<math expression>
@@ -178,57 +138,17 @@ class Math(callbacks.Plugin):
         crash to the bot with something like '10**10**10**10'.  One consequence
         is that large values such as '10**24' might not be exact.
         """
-        try:
-            text = str(text)
-        except UnicodeEncodeError:
-            irc.error(_("There's no reason you should have fancy non-ASCII "
-                            "characters in your mathematical expression. "
-                            "Please remove them."))
-            return
-        if self._calc_match_forbidden_chars.match(text):
-            # Note: this is important to keep this to forbid usage of
-            # __builtins__
-            irc.error(_('There\'s really no reason why you should have '
-                           'underscores or brackets in your mathematical '
-                           'expression.  Please remove them.'))
-            return
-        text = self._calc_remover(text)
-        if 'lambda' in text:
-            irc.error(_('You can\'t use lambda in this command.'))
-            return
-        text = text.lower()
-        def handleMatch(m):
-            s = m.group(1)
-            if s.startswith('0x'):
-                i = int(s, 16)
-            elif s.startswith('0') and '.' not in s:
-                try:
-                    i = int(s, 8)
-                except ValueError:
-                    i = int(s)
-            else:
-                i = float(s)
-            x = complex(i)
-            if x.imag == 0:
-                x = x.real
-                # Need to use string-formatting here instead of str() because
-                # use of str() on large numbers loses information:
-                # str(float(33333333333333)) => '3.33333333333e+13'
-                # float('3.33333333333e+13') => 33333333333300.0
-                return '%.16f' % x
-            return str(x)
-        text = self._mathRe.sub(handleMatch, text)
         try:
             self.log.info('evaluating %q from %s', text, msg.prefix)
-            x = complex(eval(text, self._mathSafeEnv, self._mathSafeEnv))
+            x = complex(safe_eval(text, allow_ints=False))
             irc.reply(self._complexToString(x))
         except OverflowError:
             maxFloat = math.ldexp(0.9999999999999999, 1024)
             irc.error(_('The answer exceeded %s or so.') % maxFloat)
-        except TypeError:
-            irc.error(_('Something in there wasn\'t a valid number.'))
+        except InvalidNode as e:
+            irc.error(_('Invalid syntax: %s') % e.args[0])
         except NameError as e:
-            irc.error(_('%s is not a defined function.') % str(e).split()[1])
+            irc.error(_('%s is not a defined function.') % e.args[0])
         except Exception as e:
             irc.error(str(e))
     calc = wrap(calc, ['text'])
@@ -241,28 +161,15 @@ class Math(callbacks.Plugin):
         math, and can thus cause the bot to suck up CPU.  Hence it requires
         the 'trusted' capability to use.
         """
-        if self._calc_match_forbidden_chars.match(text):
-            # Note: this is important to keep this to forbid usage of
-            # __builtins__
-            irc.error(_('There\'s really no reason why you should have '
-                           'underscores or brackets in your mathematical '
-                           'expression.  Please remove them.'))
-            return
-        # This removes spaces, too, but we'll leave the removal of _[] for
-        # safety's sake.
-        text = self._calc_remover(text)
-        if 'lambda' in text:
-            irc.error(_('You can\'t use lambda in this command.'))
-            return
-        text = text.replace('lambda', '')
         try:
             self.log.info('evaluating %q from %s', text, msg.prefix)
-            irc.reply(str(eval(text, self._mathEnv, self._mathEnv)))
+            x = safe_eval(text, allow_ints=True)
+            irc.reply(str(x))
         except OverflowError:
             maxFloat = math.ldexp(0.9999999999999999, 1024)
             irc.error(_('The answer exceeded %s or so.') % maxFloat)
-        except TypeError:
-            irc.error(_('Something in there wasn\'t a valid number.'))
+        except InvalidNode as e:
+            irc.error(_('Invalid syntax: %s') % e.args[0])
         except NameError as e:
             irc.error(_('%s is not a defined function.') % str(e).split()[1])
         except Exception as e:
@@ -286,8 +193,8 @@ class Math(callbacks.Plugin):
                     x = abs(x)
                 stack.append(x)
             except ValueError: # Not a float.
-                if arg in self._mathSafeEnv:
-                    f = self._mathSafeEnv[arg]
+                if arg in SAFE_ENV:
+                    f = SAFE_ENV[arg]
                     if callable(f):
                         called = False
                         arguments = []
@@ -310,7 +217,7 @@ class Math(callbacks.Plugin):
                     arg1 = stack.pop()
                     s = '%s%s%s' % (arg1, arg, arg2)
                     try:
-                        stack.append(eval(s, self._mathSafeEnv, self._mathSafeEnv))
+                        stack.append(safe_eval(s, allow_ints=False))
                     except SyntaxError:
                         irc.error(format(_('%q is not a defined function.'),
                                          arg))

programming_language: Python
filename: test.py
change_type: ModificationType.MODIFY
diff: @@ -91,9 +91,6 @@ class MathTestCase(PluginTestCase):
         self.assertError('base 4 4')
         self.assertError('base 10 12 A')
 
-        print()
-        print("If we have not fixed a bug with Math.base, the following ")
-        print("tests will hang the test-suite.")
         self.assertRegexp('base 2 10 [base 10 2 -12]', '-12')
         self.assertRegexp('base 16 2 [base 2 16 -110101]', '-110101')
 
@@ -117,7 +114,10 @@ class MathTestCase(PluginTestCase):
         self.assertError('calc factorial(20000)')
 
     def testCalcNoNameError(self):
-        self.assertNotRegexp('calc foobar(x)', 'NameError')
+        self.assertRegexp('calc foobar(x)', 'foobar is not a defined function')
+
+    def testCalcInvalidNode(self):
+        self.assertRegexp('calc {"foo": "bar"}', 'Illegal construct Dict')
 
     def testCalcImaginary(self):
         self.assertResponse('calc 3 + sqrt(-1)', '3+i')

programming_language: CoffeeScript