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Issue #17997: Change behavior of `ssl.match_hostname()` to follow RFC 6125,

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for security reasons.  It now doesn't match multiple wildcards nor wildcards
inside IDN fragments.
This commit is contained in:
Georg Brandl 2013-10-27 07:16:53 +01:00
parent ca580f4ec1
commit 72c98d3a76
4 changed files with 97 additions and 32 deletions
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72
Lib/ssl.py
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@ -129,31 +129,59 @@ class CertificateError(ValueError):
pass
def _dnsname_to_pat(dn, max_wildcards=1):
def _dnsname_match(dn, hostname, max_wildcards=1):
"""Matching according to RFC 6125, section 6.4.3
http://tools.ietf.org/html/rfc6125#section-6.4.3
"""
pats = []
for frag in dn.split(r'.'):
if frag.count('*') > max_wildcards:
# Issue #17980: avoid denials of service by refusing more
# than one wildcard per fragment. A survey of established
# policy among SSL implementations showed it to be a
# reasonable choice.
raise CertificateError(
"too many wildcards in certificate DNS name: " + repr(dn))
if frag == '*':
# When '*' is a fragment by itself, it matches a non-empty dotless
# fragment.
pats.append('[^.]+')
else:
# Otherwise, '*' matches any dotless fragment.
frag = re.escape(frag)
pats.append(frag.replace(r'\*', '[^.]*'))
return re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
if not dn:
return False
leftmost, *remainder = dn.split(r'.')
wildcards = leftmost.count('*')
if wildcards > max_wildcards:
# Issue #17980: avoid denials of service by refusing more
# than one wildcard per fragment. A survery of established
# policy among SSL implementations showed it to be a
# reasonable choice.
raise CertificateError(
"too many wildcards in certificate DNS name: " + repr(dn))
# speed up common case w/o wildcards
if not wildcards:
return dn.lower() == hostname.lower()
# RFC 6125, section 6.4.3, subitem 1.
# The client SHOULD NOT attempt to match a presented identifier in which
# the wildcard character comprises a label other than the left-most label.
if leftmost == '*':
# When '*' is a fragment by itself, it matches a non-empty dotless
# fragment.
pats.append('[^.]+')
elif leftmost.startswith('xn--') or hostname.startswith('xn--'):
# RFC 6125, section 6.4.3, subitem 3.
# The client SHOULD NOT attempt to match a presented identifier
# where the wildcard character is embedded within an A-label or
# U-label of an internationalized domain name.
pats.append(re.escape(leftmost))
else:
# Otherwise, '*' matches any dotless string, e.g. www*
pats.append(re.escape(leftmost).replace(r'\*', '[^.]*'))
# add the remaining fragments, ignore any wildcards
for frag in remainder:
pats.append(re.escape(frag))
pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
return pat.match(hostname)
def match_hostname(cert, hostname):
"""Verify that *cert* (in decoded format as returned by
SSLSocket.getpeercert()) matches the *hostname*. RFC 2818 rules
are mostly followed, but IP addresses are not accepted for *hostname*.
SSLSocket.getpeercert()) matches the *hostname*. RFC 2818 and RFC 6125
rules are followed, but IP addresses are not accepted for *hostname*.
CertificateError is raised on failure. On success, the function
returns nothing.
@ -164,7 +192,7 @@ def match_hostname(cert, hostname):
san = cert.get('subjectAltName', ())
for key, value in san:
if key == 'DNS':
if _dnsname_to_pat(value).match(hostname):
if _dnsname_match(value, hostname):
return
dnsnames.append(value)
if not dnsnames:
@ -175,7 +203,7 @@ def match_hostname(cert, hostname):
# XXX according to RFC 2818, the most specific Common Name
# must be used.
if key == 'commonName':
if _dnsname_to_pat(value).match(hostname):
if _dnsname_match(value, hostname):
return
dnsnames.append(value)
if len(dnsnames) > 1: