A Chrome extension release check that diffs only the permission arrays misses a content script moving to the MAIN world: compare every content_scripts entry whole, with defaults filled in, and flag each new MAIN entry · id PC-261
· checked_on 2026-11-13
· license CC-BY-4.0
1) Fill in the documented defaults of every content_scripts entry (world ISOLATED, run_at document_idle, all_frames, match_about_blank and match_origin_as_fallback false), so an omitted key equals its default and is no false change. 2) Diff each entry as a whole object; compare match and glob lists as sets, but keep js and css in order (that is the injection order). 3) Independent of order, flag every MAIN entry in the new manifest that is not an identical MAIN entry in the old one: a moved script, a new MAIN script and a MAIN script with wider matches all need a review. 4) Refuse input you cannot judge (content_scripts or a permission key that is not a list, an unknown world or run_at, a wrongly typed field) instead of reading it as 'no change'. 5) If MAIN is intended, write down which page interaction needs it and test that in a browser; a static diff only says that something changed. 6) Check chrome.scripting.registerContentScripts and executeScript calls in code too: they take the same world option and do not show up in manifest.json.
#!/usr/bin/env python3
"""mv3_content_script_diff.py - did a Chrome MV3 release change what a content
script can touch, even though the permission arrays stayed the same?
A release check that only diffs permissions / host_permissions misses a content
script that moves from the ISOLATED world to the MAIN world: "world" is a field
of each content_scripts entry, not a permission. Chrome docs: world "Defaults to
"ISOLATED"" and "Choosing the "MAIN" world means the script will share the
execution environment with the host page's JavaScript."
usage: python3 -I mv3_content_script_diff.py --selftest
python3 -I mv3_content_script_diff.py OLD_manifest.json NEW_manifest.json
What it does: fills in the documented defaults of every content_scripts entry
(so an omitted key equals its default and is no false change), diffs each entry
as a whole, and flags every MAIN entry in the new manifest that has no identical
MAIN entry in the old one. That last rule does not depend on entry order, so a
swap of two entries cannot hide a script that moved to MAIN.
Match-pattern and glob lists are compared as sets; js and css keep their order
(injection order). No network.
Output, one line per finding:
perm <key> +x / -x a permission array changed
cs[i] <field>: old -> new a field of entry i changed (paired by position)
cs[i] added / removed an entry appeared or disappeared
NEW-MAIN cs[i] entry i of the new manifest runs in MAIN and is
not an unchanged MAIN entry of the old manifest
Exit 0 = no change, 1 = any change (review it; NEW-MAIN needs a reason and a
browser test), 2 = usage or bad input (not an object, a permission key or
content_scripts that is not a list, an unknown world, a wrongly typed field).
"""
import json
import sys
DEFAULTS = {'world': 'ISOLATED', 'run_at': 'document_idle', 'all_frames': False,
'match_about_blank': False, 'match_origin_as_fallback': False,
'js': [], 'css': [], 'matches': [], 'exclude_matches': [],
'include_globs': [], 'exclude_globs': []}
SET_FIELDS = ('matches', 'exclude_matches', 'include_globs', 'exclude_globs')
LIST_FIELDS = SET_FIELDS + ('js', 'css')
BOOL_FIELDS = ('all_frames', 'match_about_blank', 'match_origin_as_fallback')
RUN_AT = ('document_start', 'document_end', 'document_idle')
PERM_KEYS = ('permissions', 'optional_permissions', 'host_permissions',
'optional_host_permissions')
def _strlist(v, what):
if not isinstance(v, list) or not all(isinstance(x, str) for x in v):
raise ValueError('%s must be a list of strings' % what)
return v
def _norm(cs, i):
if not isinstance(cs, dict):
raise ValueError('content_scripts[%d] is not an object' % i)
out = dict(DEFAULTS)
out.update(cs)
if out['world'] not in ('ISOLATED', 'MAIN'):
raise ValueError('content_scripts[%d]: unknown world %r' % (i, out['world']))
if out['run_at'] not in RUN_AT:
raise ValueError('content_scripts[%d]: unknown run_at %r' % (i, out['run_at']))
for f in BOOL_FIELDS:
if not isinstance(out[f], bool):
raise ValueError('content_scripts[%d]: %s must be true/false' % (i, f))
for f in LIST_FIELDS:
_strlist(out[f], 'content_scripts[%d].%s' % (i, f))
for f in SET_FIELDS:
out[f] = sorted(set(out[f]))
return out
def _entries(m):
cs = m.get('content_scripts', [])
if not isinstance(cs, list):
raise ValueError('content_scripts must be a list')
return [_norm(c, i) for i, c in enumerate(cs)]
def _key(e):
return json.dumps(e, sort_keys=True)
def diff(old, new):
if not isinstance(old, dict) or not isinstance(new, dict):
raise ValueError('manifest is not a JSON object')
found = []
for k in PERM_KEYS:
a = set(_strlist(old.get(k, []), k))
b = set(_strlist(new.get(k, []), k))
found += ['perm %s +%s' % (k, x) for x in sorted(b - a)]
found += ['perm %s -%s' % (k, x) for x in sorted(a - b)]
oc, nc = _entries(old), _entries(new)
for i in range(max(len(oc), len(nc))):
if i >= len(oc):
found.append('cs[%d] added' % i)
elif i >= len(nc):
found.append('cs[%d] removed' % i)
else:
for f in sorted(set(oc[i]) | set(nc[i])):
if oc[i].get(f) != nc[i].get(f):
found.append('cs[%d] %s: %s -> %s' % (
i, f, json.dumps(oc[i].get(f)), json.dumps(nc[i].get(f))))
old_main = {_key(e) for e in oc if e['world'] == 'MAIN'}
for i, e in enumerate(nc):
if e['world'] == 'MAIN' and _key(e) not in old_main:
found.append('NEW-MAIN cs[%d]' % i)
return found
def array_only(old, new):
return [f for f in diff(old, new) if f.startswith('perm ')]
def selftest():
fails = []
def eq(name, got, want):
if got != want:
fails.append('%s: %r != %r' % (name, got, want))
def cp(x):
return json.loads(json.dumps(x))
a = {'matches': ['https://example.com/*'], 'js': ['a.js']}
b = {'matches': ['https://example.org/*'], 'js': ['b.js']}
base = {'manifest_version': 3, 'name': 'x', 'version': '1.0',
'permissions': ['storage'], 'host_permissions': ['https://example.com/*'],
'content_scripts': [cp(a)]}
main = cp(base)
main['content_scripts'][0]['world'] = 'MAIN'
# The reported case: only world changed. Array-only sees nothing.
eq('array-only blind', array_only(base, main), [])
eq('world change', diff(base, main),
['cs[0] world: "ISOLATED" -> "MAIN"', 'NEW-MAIN cs[0]'])
explicit = cp(base)
explicit['content_scripts'][0].update(world='ISOLATED', run_at='document_idle',
all_frames=False)
eq('explicit defaults = omitted', diff(base, explicit), [])
eq('same', diff(base, base), [])
eq('MAIN stays MAIN', diff(main, main), [])
eq('MAIN -> ISOLATED', diff(main, base), ['cs[0] world: "MAIN" -> "ISOLATED"'])
added = cp(base)
added['content_scripts'].append(dict(b, world='MAIN'))
eq('added MAIN', diff(base, added), ['cs[1] added', 'NEW-MAIN cs[1]'])
eq('removed', diff(added, base), ['cs[1] removed'])
none = {k: v for k, v in base.items() if k != 'content_scripts'}
eq('first content script, MAIN', diff(none, main), ['cs[0] added', 'NEW-MAIN cs[0]'])
# Swap: old [a MAIN, b ISOLATED], new [b MAIN, a ISOLATED]. Position pairing
# sees MAIN->MAIN and ISOLATED->ISOLATED; b still moved to MAIN.
old_sw = dict(none, content_scripts=[dict(a, world='MAIN'), cp(b)])
new_sw = dict(none, content_scripts=[dict(b, world='MAIN'), cp(a)])
eq('swap hides nothing', [f for f in diff(old_sw, new_sw) if f.startswith('NEW-MAIN')],
['NEW-MAIN cs[0]'])
eq('reorder only', [f for f in diff(old_sw, dict(none, content_scripts=[cp(b), dict(a, world='MAIN')]))
if f.startswith('NEW-MAIN')], [])
# A MAIN entry that widens its matches is a new MAIN surface too.
wide = cp(main)
wide['content_scripts'][0]['matches'] = ['<all_urls>']
eq('MAIN widened', diff(main, wide)[-1], 'NEW-MAIN cs[0]')
reordered = cp(base)
reordered['content_scripts'][0]['matches'] = ['https://example.com/*', 'https://a.example/*']
r2 = cp(base)
r2['content_scripts'][0]['matches'] = ['https://a.example/*', 'https://example.com/*']
eq('match order is not a change', diff(reordered, r2), [])
js2 = cp(base)
js2['content_scripts'][0]['js'] = ['z.js', 'a.js']
js3 = cp(base)
js3['content_scripts'][0]['js'] = ['a.js', 'z.js']
eq('js order is a change', len(diff(js2, js3)), 1)
frames = cp(base)
frames['content_scripts'][0]['all_frames'] = True
eq('all_frames', diff(base, frames), ['cs[0] all_frames: false -> true'])
perm = cp(base)
perm['permissions'].append('scripting')
eq('perm', diff(base, perm), ['perm permissions +scripting'])
bad = [
dict(none, content_scripts=[{'world': 'PAGE'}]),
dict(none, content_scripts=['x']),
dict(none, content_scripts={'world': 'MAIN'}),
dict(none, content_scripts={}),
dict(none, content_scripts=[5]),
dict(none, content_scripts=[dict(a, world=None)]),
dict(none, content_scripts=[dict(a, all_frames='true')]),
dict(none, content_scripts=[dict(a, run_at='document_ready')]),
dict(none, content_scripts=[dict(a, js='a.js')]),
dict(none, permissions='storage'),
[],
]
for n, m in enumerate(bad):
try:
diff(base, m)
fails.append('bad %d accepted' % n)
except ValueError:
pass
try:
diff(m, base)
fails.append('bad %d accepted as old' % n)
except ValueError:
pass
for f in fails:
print('FAIL', f)
print('pass' if not fails else 'FAIL')
return 0 if not fails else 1
def main(argv):
if argv[1:] == ['--selftest']:
return selftest()
if len(argv) != 3:
print(__doc__.split('\n\n')[2], file=sys.stderr)
return 2
try:
with open(argv[1], encoding='utf-8') as fa, open(argv[2], encoding='utf-8') as fb:
found = diff(json.load(fa), json.load(fb))
except (OSError, ValueError) as e:
print('error:', e, file=sys.stderr)
return 2
for line in found:
print(line)
if not found:
print('no change')
return 1 if found else 0
if __name__ == '__main__':
sys.exit(main(sys.argv))
An agent builds or updates a Chrome Manifest V3 extension, often from a template, and runs a release check before it ships: did permissions or host_permissions change between the old and the new manifest.json? If not, the release is treated as harmless.
The check reports zero changes, yet a content script now runs inside the page's own JavaScript environment. Reported case (synthetic manifest pair): only content_scripts[0].world changed from ISOLATED to MAIN, with the same script and host pattern; an array-only check saw 0 changes, a compare of the whole declaration saw 1. No install warning and no error appears.
world is a field of each content_scripts entry, not a permission. Chrome's manifest reference: '"world" - ISOLATED | MAIN Optional. The JavaScript world for a script to execute within. Defaults to "ISOLATED", which is the execution environment unique to the content script. Choosing the "MAIN" world means the script will share the execution environment with the host page's JavaScript.' and 'Warning: There are risks involved when using the "MAIN" world. The host page can access and interfere with the injected script.' The same entry carries other reach-changing fields that no permission array shows: matches, all_frames, match_about_blank, match_origin_as_fallback, run_at. Comparing entries only by position has a second gap: if two entries swap places and one of them becomes MAIN, each position still reads MAIN -> MAIN and ISOLATED -> ISOLATED.
Save the snippet as mv3_content_script_diff.py and run `python3 -I mv3_content_script_diff.py --selftest` (no network). Pass: the last line is `pass` and the exit code is 0. It asserts: the reported case (only world ISOLATED -> MAIN) is invisible to an array-only diff and gives `NEW-MAIN cs[0]`; explicit defaults equal omitted keys; a swap of two entries where one becomes MAIN is still flagged; a pure reorder is not; a MAIN entry with wider matches is flagged; match order is no change but js order is; added and removed entries, all_frames and a permission change are reported; and bad input on either side (non-list content_scripts or permissions, unknown world or run_at, string booleans, non-object entries) is refused. On real data: `python3 -I mv3_content_script_diff.py old/manifest.json new/manifest.json`; exit 0 = no change, 1 = review the listed lines, 2 = bad input. Not covered: a real browser run, and content scripts registered from code.
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