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gh-145599: Reject control characters in `http.cookies.Morsel.update()` and `http.cookies.BaseCookie.js_output` by StanFromIreland · Pull Request #145600 · python/cpython · GitHub

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gh-145599: Reject control characters in http.cookies.Morsel.update() and http.cookies.BaseCookie.js_output #145600

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Merged
vstinner merged 7 commits into from
Mar 16, 2026
Conversation 24 Commits 7 Checks 59 Files changed
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gh-145599: Reject control characters in http.cookies.Morsel.update() and http.cookies.BaseCookie.js_output #145600

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87d0887
Patch
StanFromIreland Mar 6, 2026
63a3b59
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StanFromIreland Mar 6, 2026
dce754d
Seth's review, fix blurb
StanFromIreland Mar 6, 2026
bb54e28
Convert to fstr, move check
StanFromIreland Mar 13, 2026
ae804e4
Add reference to news entry.
StanFromIreland Mar 15, 2026
ba6713e
Victor's request
StanFromIreland Mar 16, 2026
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StanFromIreland Mar 16, 2026
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24 changes: 20 additions & 4 deletions Lib/http/cookies.py
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Original file line number Diff line number Diff line change
Expand Up @@ -337,9 +337,16 @@ def update(self, values):
key = key.lower()
if key not in self._reserved:
raise CookieError("Invalid attribute %r" % (key,))
if _has_control_character(key, val):
raise CookieError("Control characters are not allowed in "
f"cookies {key!r} {val!r}")
data[key] = val
dict.update(self, data)

def __ior__(self, values):
self.update(values)
return self
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def isReservedKey(self, K):
return K.lower() in self._reserved

Expand All @@ -365,9 +372,15 @@ def __getstate__(self):
}

def __setstate__(self, state):
self._key = state['key']
self._value = state['value']
self._coded_value = state['coded_value']
key = state['key']
value = state['value']
coded_value = state['coded_value']
if _has_control_character(key, value, coded_value):
raise CookieError("Control characters are not allowed in cookies "
f"{key!r} {value!r} {coded_value!r}")
self._key = key
self._value = value
self._coded_value = coded_value

def output(self, attrs=None, header="Set-Cookie:"):
return "%s %s" % (header, self.OutputString(attrs))
Expand All @@ -379,13 +392,16 @@ def __repr__(self):

def js_output(self, attrs=None):
# Print javascript
output_string = self.OutputString(attrs)
if _has_control_character(output_string):
raise CookieError("Control characters are not allowed in cookies")
return """
<script type="text/javascript">
<!-- begin hiding
document.cookie = \"%s\";
// end hiding -->
</script>
""" % (self.OutputString(attrs).replace('"', r'\"'))
""" % (output_string.replace('"', r'\"'))

def OutputString(self, attrs=None):
# Build up our result
Expand Down
38 changes: 38 additions & 0 deletions Lib/test/test_http_cookies.py
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Original file line number Diff line number Diff line change
Expand Up @@ -604,6 +604,14 @@ def test_control_characters(self):
with self.assertRaises(cookies.CookieError):
morsel["path"] = c0

# .__setstate__()
with self.assertRaises(cookies.CookieError):
morsel.__setstate__({'key': c0, 'value': 'val', 'coded_value': 'coded'})
with self.assertRaises(cookies.CookieError):
morsel.__setstate__({'key': 'key', 'value': c0, 'coded_value': 'coded'})
with self.assertRaises(cookies.CookieError):
morsel.__setstate__({'key': 'key', 'value': 'val', 'coded_value': c0})

# .setdefault()
with self.assertRaises(cookies.CookieError):
morsel.setdefault("path", c0)
Expand All @@ -618,6 +626,18 @@ def test_control_characters(self):
with self.assertRaises(cookies.CookieError):
morsel.set("path", "val", c0)

# .update()
with self.assertRaises(cookies.CookieError):
morsel.update({"path": c0})
with self.assertRaises(cookies.CookieError):
morsel.update({c0: "val"})

# .__ior__()
with self.assertRaises(cookies.CookieError):
morsel |= {"path": c0}
with self.assertRaises(cookies.CookieError):
morsel |= {c0: "val"}

def test_control_characters_output(self):
# Tests that even if the internals of Morsel are modified
# that a call to .output() has control character safeguards.
Expand All @@ -638,6 +658,24 @@ def test_control_characters_output(self):
with self.assertRaises(cookies.CookieError):
cookie.output()

# Tests that .js_output() also has control character safeguards.
for c0 in support.control_characters_c0():
morsel = cookies.Morsel()
morsel.set("key", "value", "coded-value")
morsel._key = c0 # Override private variable.
cookie = cookies.SimpleCookie()
cookie["cookie"] = morsel
with self.assertRaises(cookies.CookieError):
cookie.js_output()

morsel = cookies.Morsel()
morsel.set("key", "value", "coded-value")
morsel._coded_value = c0 # Override private variable.
cookie = cookies.SimpleCookie()
cookie["cookie"] = morsel
with self.assertRaises(cookies.CookieError):
cookie.js_output()


def load_tests(loader, tests, pattern):
tests.addTest(doctest.DocTestSuite(cookies))
Expand Down
4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Security/2026-03-06-17-03-38.gh-issue-145599.kchwZV.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Reject control characters in :class:`http.cookies.Morsel`
:meth:`~http.cookies.Morsel.update` and
:meth:`~http.cookies.BaseCookie.js_output`.
This addresses :cve:`2026-3644`.

vstinner Mar 16, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Are you sure about the CVE number?

StanFromIreland Mar 16, 2026 •
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

This one has been reserved for it, see the sidebar of the GHSA.
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