---
 Doc/library/email.utils.rst                                              |   24 +++
 Lib/email/utils.py                                                       |   66 +++++++++-
 Misc/NEWS.d/next/Security/2023-06-13-20-52-24.gh-issue-102988.Kei7Vf.rst |    4 
 3 files changed, 88 insertions(+), 6 deletions(-)

--- a/Doc/library/email.utils.rst
+++ b/Doc/library/email.utils.rst
@@ -63,6 +63,11 @@ There are several useful utilities provi
    :func:`time.mktime`; otherwise ``None`` will be returned.  Note that indexes 6,
    7, and 8 of the result tuple are not usable.
 
+   .. versionchanged:: 3.12
+      For security reasons, addresses that were ambiguous and could parse into
+      multiple different addresses now cause ``('', '')`` to be returned
+      instead of only one of the *potential* addresses.
+
 
 .. function:: parsedate_tz(date)
 
@@ -103,6 +108,25 @@ There are several useful utilities provi
 
    .. versionadded:: 2.4
 
+   When parsing fails for a single fieldvalue, a 2-tuple of ``('', '')``
+   is returned in its place.  Other errors in parsing the list of
+   addresses such as a fieldvalue seemingly parsing into multiple
+   addresses may result in a list containing a single empty 2-tuple
+   ``[('', '')]`` being returned rather than returning potentially
+   invalid output.
+
+   Example malformed input parsing:
+
+   .. doctest::
+
+      >>> from email.utils import getaddresses
+      >>> getaddresses(['alice@example.com <bob@example.com>', 'me@example.com'])
+      [('', '')]
+
+   .. versionchanged:: 3.12
+      The 2-tuple of ``('', '')`` in the returned values when parsing
+      fails were added as to address a security issue.
+
 
 .. function:: make_msgid([idstring])
 
--- a/Lib/email/utils.py
+++ b/Lib/email/utils.py
@@ -101,11 +101,56 @@ def formataddr(pair):
 
 
 
+def _pre_parse_validation(email_header_fields):
+    accepted_values = []
+    for v in email_header_fields:
+        s = v.replace('\\(', '').replace('\\)', '')
+        if s.count('(') != s.count(')'):
+            v = "('', '')"
+        accepted_values.append(v)
+
+    return accepted_values
+
+
+
+def _post_parse_validation(parsed_email_header_tuples):
+    accepted_values = []
+    # The parser would have parsed a correctly formatted domain-literal
+    # The existence of an [ after parsing indicates a parsing failure
+    for v in parsed_email_header_tuples:
+        if '[' in v[1]:
+            v = ('', '')
+        accepted_values.append(v)
+
+    return accepted_values
+
+
+
 def getaddresses(fieldvalues):
-    """Return a list of (REALNAME, EMAIL) for each fieldvalue."""
-    all = COMMASPACE.join(fieldvalues)
+    """Return a list of (REALNAME, EMAIL) or ('','') for each fieldvalue.
+
+    When parsing fails for a fieldvalue, a 2-tuple of ('', '') is returned in
+    its place.
+
+    If the resulting list of parsed address is not the same as the number of
+    fieldvalues in the input list a parsing error has occurred.  A list
+    containing a single empty 2-tuple [('', '')] is returned in its place.
+    This is done to avoid invalid output.
+    """
+    fieldvalues = [str(v) for v in fieldvalues]
+    fieldvalues = _pre_parse_validation(fieldvalues)
+    all = COMMASPACE.join(v for v in fieldvalues)
     a = _AddressList(all)
-    return a.addresslist
+    result = _post_parse_validation(a.addresslist)
+
+    n = 0
+    for v in fieldvalues:
+        n += v.count(',') + 1
+
+    if len(result) != n:
+        return [('', '')]
+
+    return result
 
 
 
@@ -217,9 +262,18 @@ def parseaddr(addr):
     Return a tuple of realname and email address, unless the parse fails, in
     which case return a 2-tuple of ('', '').
     """
-    addrs = _AddressList(addr).addresslist
-    if not addrs:
-        return '', ''
+    if isinstance(addr, list):
+        addr = addr[0]
+
+    if not isinstance(addr, str):
+        return ('', '')
+
+    addr = _pre_parse_validation([addr])[0]
+    addrs = _post_parse_validation(_AddressList(addr).addresslist)
+
+    if not addrs or len(addrs) > 1:
+        return ('', '')
+
     return addrs[0]
 
 
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2023-06-13-20-52-24.gh-issue-102988.Kei7Vf.rst
@@ -0,0 +1,4 @@
+CVE-2023-27043: Prevent :func:`email.utils.parseaddr`
+and :func:`email.utils.getaddresses` from returning the realname portion of an
+invalid RFC2822 email header in the email address portion of the 2-tuple
+returned after being parsed by :class:`email._parseaddr.AddressList`.