/usr/share/pyshared/M2Crypto/SSL/Checker.py is in python-m2crypto 0.21.1-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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SSL peer certificate checking routines
Copyright (c) 2004-2007 Open Source Applications Foundation.
All rights reserved.
Copyright 2008 Heikki Toivonen. All rights reserved.
"""
__all__ = ['SSLVerificationError', 'NoCertificate', 'WrongCertificate',
'WrongHost', 'Checker']
from M2Crypto import util, EVP, m2
import re
class SSLVerificationError(Exception):
pass
class NoCertificate(SSLVerificationError):
pass
class WrongCertificate(SSLVerificationError):
pass
class WrongHost(SSLVerificationError):
def __init__(self, expectedHost, actualHost, fieldName='commonName'):
"""
This exception will be raised if the certificate returned by the
peer was issued for a different host than we tried to connect to.
This could be due to a server misconfiguration or an active attack.
@param expectedHost: The name of the host we expected to find in the
certificate.
@param actualHost: The name of the host we actually found in the
certificate.
@param fieldName: The field name where we noticed the error. This
should be either 'commonName' or 'subjectAltName'.
"""
if fieldName not in ('commonName', 'subjectAltName'):
raise ValueError('Unknown fieldName, should be either commonName or subjectAltName')
SSLVerificationError.__init__(self)
self.expectedHost = expectedHost
self.actualHost = actualHost
self.fieldName = fieldName
def __str__(self):
s = 'Peer certificate %s does not match host, expected %s, got %s' \
% (self.fieldName, self.expectedHost, self.actualHost)
if isinstance(s, unicode):
s = s.encode('utf8')
return s
class Checker:
numericIpMatch = re.compile('^[0-9]+(\.[0-9]+)*$')
def __init__(self, host=None, peerCertHash=None, peerCertDigest='sha1'):
self.host = host
self.fingerprint = peerCertHash
self.digest = peerCertDigest
def __call__(self, peerCert, host=None):
if peerCert is None:
raise NoCertificate('peer did not return certificate')
if host is not None:
self.host = host
if self.fingerprint:
if self.digest not in ('sha1', 'md5'):
raise ValueError('unsupported digest "%s"' %(self.digest))
if (self.digest == 'sha1' and len(self.fingerprint) != 40) or \
(self.digest == 'md5' and len(self.fingerprint) != 32):
raise WrongCertificate('peer certificate fingerprint length does not match')
der = peerCert.as_der()
md = EVP.MessageDigest(self.digest)
md.update(der)
digest = md.final()
if util.octx_to_num(digest) != int(self.fingerprint, 16):
raise WrongCertificate('peer certificate fingerprint does not match')
if self.host:
hostValidationPassed = False
self.useSubjectAltNameOnly = False
# subjectAltName=DNS:somehost[, ...]*
try:
subjectAltName = peerCert.get_ext('subjectAltName').get_value()
if self._splitSubjectAltName(self.host, subjectAltName):
hostValidationPassed = True
elif self.useSubjectAltNameOnly:
raise WrongHost(expectedHost=self.host,
actualHost=subjectAltName,
fieldName='subjectAltName')
except LookupError:
pass
# commonName=somehost[, ...]*
if not hostValidationPassed:
hasCommonName = False
commonNames = ''
for entry in peerCert.get_subject().get_entries_by_nid(m2.NID_commonName):
hasCommonName = True
commonName = entry.get_data().as_text()
if not commonNames:
commonNames = commonName
else:
commonNames += ',' + commonName
if self._match(self.host, commonName):
hostValidationPassed = True
break
if not hasCommonName:
raise WrongCertificate('no commonName in peer certificate')
if not hostValidationPassed:
raise WrongHost(expectedHost=self.host,
actualHost=commonNames,
fieldName='commonName')
return True
def _splitSubjectAltName(self, host, subjectAltName):
"""
>>> check = Checker()
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:my.example.com')
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:*.example.com')
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:m*.example.com')
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:m*ample.com')
False
>>> check.useSubjectAltNameOnly
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:m*ample.com, othername:<unsupported>')
False
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:m*ample.com, DNS:my.example.org')
False
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:m*ample.com, DNS:my.example.com')
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='DNS:my.example.com, DNS:my.example.org')
True
>>> check.useSubjectAltNameOnly
True
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='')
False
>>> check._splitSubjectAltName(host='my.example.com', subjectAltName='othername:<unsupported>')
False
>>> check.useSubjectAltNameOnly
False
"""
self.useSubjectAltNameOnly = False
for certHost in subjectAltName.split(','):
certHost = certHost.lower().strip()
if certHost[:4] == 'dns:':
self.useSubjectAltNameOnly = True
if self._match(host, certHost[4:]):
return True
return False
def _match(self, host, certHost):
"""
>>> check = Checker()
>>> check._match(host='my.example.com', certHost='my.example.com')
True
>>> check._match(host='my.example.com', certHost='*.example.com')
True
>>> check._match(host='my.example.com', certHost='m*.example.com')
True
>>> check._match(host='my.example.com', certHost='m*.EXAMPLE.com')
True
>>> check._match(host='my.example.com', certHost='m*ample.com')
False
>>> check._match(host='my.example.com', certHost='*.*.com')
False
>>> check._match(host='1.2.3.4', certHost='1.2.3.4')
True
>>> check._match(host='1.2.3.4', certHost='*.2.3.4')
False
>>> check._match(host='1234', certHost='1234')
True
"""
# XXX See RFC 2818 and 3280 for matching rules, this is may not
# XXX yet be complete.
host = host.lower()
certHost = certHost.lower()
if host == certHost:
return True
if certHost.count('*') > 1:
# Not sure about this, but being conservative
return False
if self.numericIpMatch.match(host) or \
self.numericIpMatch.match(certHost.replace('*', '')):
# Not sure if * allowed in numeric IP, but think not.
return False
if certHost.find('\\') > -1:
# Not sure about this, maybe some encoding might have these.
# But being conservative for now, because regex below relies
# on this.
return False
# Massage certHost so that it can be used in regex
certHost = certHost.replace('.', '\.')
certHost = certHost.replace('*', '[^\.]*')
if re.compile('^%s$' %(certHost)).match(host):
return True
return False
if __name__ == '__main__':
import doctest
doctest.testmod()
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