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Feature/ssl match hostname 17997 #2

Merged
merged 2 commits into from

2 participants

@abadger

There's apparently another security issue in the python3 match_hostname code. No CVE has been issued for it yet:

http://bugs.python.org/issue17997#msg194950

Here's a pull request in two commits. The first updates the included match_hostname code to reflect what's in the python-3.3.3 and python-3.4 stdlib (with a minor change to preserve python2 compat). The second commit adds a check for the backports.ssl_match_hostname module from pypi: https://pypi.python.org/pypi/backports.ssl_match_hostname

If the stdlib doesn't have ssl_match_hostname but backports.ssl_match_hostname exists it uses that code. If neither one are present, then it uses the code included in setuptools.

I added the fallback in a second commit because I wasn't certain how you'd feel about that. It certainly helps us out as system packagers and system admins to have a single place to change rather than every package that's copying the match_hostname code. On the other hand, it means that users won't get any fixes before they go into the backports.ssl_match_hostname module. brandon rhodes is the owner of that module and I've done the last several releases to make sure we're current with the match_hostname security issues.

@jaraco jaraco merged commit 6360097 into jaraco:master
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Commits on Oct 28, 2013
  1. @abadger

    Update ssl_match_hostname to match new stdlib code that fixes a secur…

    abadger authored
    …ity issue with IDNA domains.
  2. @abadger

    Look for the backports-ssl_match_hostname module from pypi before usi…

    abadger authored
    …ng our bundled/backported code
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Showing with 63 additions and 22 deletions.
  1. +63 −22 setuptools/ssl_support.py
View
85 setuptools/ssl_support.py
@@ -85,33 +85,74 @@ def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
try:
from ssl import CertificateError, match_hostname
except ImportError:
+ try:
+ from backports.ssl_match_hostname import CertificateError
+ from backports.ssl_match_hostname import match_hostname
+ except ImportError:
+ CertificateError = None
+ match_hostname = None
+
+if not CertificateError:
class CertificateError(ValueError):
pass
- def _dnsname_to_pat(dn, max_wildcards=1):
+if not match_hostname:
+ 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 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))
- 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
+
+ # Ported from python3-syntax:
+ # leftmost, *remainder = dn.split(r'.')
+ parts = dn.split(r'.')
+ leftmost = parts[0]
+ remainder = parts[1:]
+
+ wildcards = leftmost.count('*')
+ if wildcards > 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))
+
+ # 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.
@@ -122,7 +163,7 @@ 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:
@@ -133,7 +174,7 @@ 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:
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