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gh-150522: anchor suffix check in http.cookiejar.domain_match #150523

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gh-150522: anchor suffix check in http.cookiejar.domain_match #150523

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5 changes: 3 additions & 2 deletions Lib/http/cookiejar.py
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Original file line number Diff line number Diff line change
Expand Up @@ -578,8 +578,9 @@ def domain_match(A, B):
if not is_HDN(A):
return False
i = A.rfind(B)
if i == -1 or i == 0:
# A does not have form NB, or N is the empty string
if i == -1 or i == 0 or i + len(B) != len(A):
# A does not have form NB, N is the empty string, or B is not a
# suffix of A (so A only contains B as an interior substring)
return False
if not B.startswith("."):
return False
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3 changes: 3 additions & 0 deletions Lib/test/test_http_cookiejar.py
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Expand Up @@ -888,6 +888,9 @@ def test_domain_match(self):
self.assertFalse(domain_match("blah.blah", ""))
self.assertFalse(domain_match("", ".rhubarb.rhubarb"))
self.assertTrue(domain_match("", ""))
# B must be a suffix of A, not just an interior substring
self.assertFalse(domain_match("www.acme.com.evil.org", ".acme.com"))
self.assertFalse(domain_match("a.b.c.com.example.net", ".c.com"))

self.assertTrue(user_domain_match("acme.com", "acme.com"))
self.assertFalse(user_domain_match("acme.com", ".acme.com"))
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-05-27-11-20-00.gh-issue-150522.Qd7Rb3.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:func:`http.cookiejar.domain_match` now requires the second domain to be a
suffix of the first instead of merely an interior substring, so a host such
as ``www.example.com.evil`` no longer domain-matches ``.example.com``.
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