diff --git a/Lib/email/_encoded_words.py b/Lib/email/_encoded_words.py
index 6795a606de037e..7c2dfb360f95ad 100644
--- a/Lib/email/_encoded_words.py
+++ b/Lib/email/_encoded_words.py
@@ -113,9 +113,14 @@ def decode_b(encoded):
# The non-alphabet characters are ignored as far as padding
# goes, but we don't know how many there are. So try without adding
# padding to see if it works.
+ #
+ # We use urlsafe_b64decode here because some mailers apparently use the
+ # urlsafe b64 alphabet, and urlsafe_b64decode will correctly decode
+ # both the urlsafe and regular alphabets.
+
try:
return (
- base64.b64decode(encoded, validate=False),
+ base64.urlsafe_b64decode(encoded),
[errors.InvalidBase64CharactersDefect()],
)
except binascii.Error:
@@ -123,7 +128,7 @@ def decode_b(encoded):
# is ignored).
try:
return (
- base64.b64decode(encoded + b'==', validate=False),
+ base64.urlsafe_b64decode(encoded + b'=='),
[errors.InvalidBase64CharactersDefect(),
errors.InvalidBase64PaddingDefect()],
)
diff --git a/Lib/email/base64mime.py b/Lib/email/base64mime.py
index a5a3f737a97b51..3363a5bc45f2d4 100644
--- a/Lib/email/base64mime.py
+++ b/Lib/email/base64mime.py
@@ -34,8 +34,8 @@
]
-from base64 import b64encode
-from binascii import b2a_base64, a2b_base64
+from base64 import b64encode, urlsafe_b64decode
+from binascii import b2a_base64
CRLF = '\r\n'
NL = '\n'
@@ -102,12 +102,15 @@ def decode(string):
base64 (like =?iso-8859-1?b?bmloISBuaWgh?=) -- please use the high
level email.header class for that functionality.
"""
+ # We use urlsafe_b64decode here because some mailers apparently use the
+ # urlsafe b64 alphabet, and urlsafe_b64decode will correctly decode both
+ # the urlsafe and regular alphabets.
if not string:
return bytes()
elif isinstance(string, str):
- return a2b_base64(string.encode('raw-unicode-escape'))
+ return urlsafe_b64decode(string.encode('raw-unicode-escape'))
else:
- return a2b_base64(string)
+ return urlsafe_b64decode(string)
# For convenience and backwards compatibility w/ standard base64 module
diff --git a/Lib/test/test_email/test__encoded_words.py b/Lib/test/test_email/test__encoded_words.py
index 1713962f94caef..2686448565bbbe 100644
--- a/Lib/test/test_email/test__encoded_words.py
+++ b/Lib/test/test_email/test__encoded_words.py
@@ -38,6 +38,14 @@ def test_missing_padding(self):
# 2 missing padding characters
self._test(b'dg', b'v', [errors.InvalidBase64PaddingDefect])
+ def test_urlsafe_alphabet(self):
+ self._test(
+ b'QW5tZWxkdW5nIE5ldHphbnNjaGx1c3MgU_xkcmluZzNwLmpwZw==',
+ b'Anmeldung Netzanschluss S\xfcdring3p.jpg',
+ [errors.InvalidBase64CharactersDefect])
+ # mix of different base64 alphabets
+ self._test(b'aGVsbG8_Pz8/', b'hello????', [errors.InvalidBase64CharactersDefect])
+
def test_invalid_character(self):
self._test(b'dm\x01k===', b'vi', [errors.InvalidBase64CharactersDefect])
diff --git a/Lib/test/test_email/test_email.py b/Lib/test/test_email/test_email.py
index b8116d073a2670..03381ea1b72b2f 100644
--- a/Lib/test/test_email/test_email.py
+++ b/Lib/test/test_email/test_email.py
@@ -4663,6 +4663,11 @@ def test_decode(self):
eq = self.assertEqual
eq(base64mime.decode(''), b'')
eq(base64mime.decode('aGVsbG8='), b'hello')
+ eq(base64mime.decode(
+ 'QW5tZWxkdW5nIE5ldHphbnNjaGx1c3MgU_xkcmluZzNwLmpwZw=='),
+ b'Anmeldung Netzanschluss S\xfcdring3p.jpg')
+ # mix of different base64 alphabets
+ eq(base64mime.decode('aGVsbG8_Pz8/'), b'hello????')
def test_encode(self):
eq = self.assertEqual
diff --git a/Misc/NEWS.d/next/Library/2025-07-19-16-59-16.gh-issue-56698.yHSmT_.rst b/Misc/NEWS.d/next/Library/2025-07-19-16-59-16.gh-issue-56698.yHSmT_.rst
new file mode 100644
index 00000000000000..d23e7eb2bd4c0e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-07-19-16-59-16.gh-issue-56698.yHSmT_.rst
@@ -0,0 +1,2 @@
+Accept urlsafe base64 in email headers, as those are sometimes created by
+email clients.
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