[3.10] gh-143930: Reject leading dashes in webbrowser URLs

(cherry picked from commit 82a24a4)

Co-authored-by: Seth Michael Larson <seth@python.org>

Author: sethmlarson

Lib/test/test_webbrowser.py

@@ -57,6 +57,11 @@ def test_open(self):
                    options=[],
                    arguments=[URL])
 
+    def test_reject_dash_prefixes(self):
+        browser = self.browser_class(name=CMD_NAME)
+        with self.assertRaises(ValueError):
+            browser.open(f"--key=val {URL}")
+
 
 class BackgroundBrowserCommandTest(CommandTestMixin, unittest.TestCase):
 

Lib/webbrowser.py

@@ -154,6 +154,12 @@ def open_new(self, url):
     def open_new_tab(self, url):
         return self.open(url, 2)
 
+    @staticmethod
+    def _check_url(url):
+        """Ensures that the URL is safe to pass to subprocesses as a parameter"""
+        if url and url.lstrip().startswith("-"):
+            raise ValueError(f"Invalid URL: {url}")
+
 
 class GenericBrowser(BaseBrowser):
     """Class for all browsers started with a command
@@ -171,6 +177,7 @@ def __init__(self, name):
 
     def open(self, url, new=0, autoraise=True):
         sys.audit("webbrowser.open", url)
+        self._check_url(url)
         cmdline = [self.name] + [arg.replace("%s", url)
                                  for arg in self.args]
         try:
@@ -191,6 +198,7 @@ def open(self, url, new=0, autoraise=True):
         cmdline = [self.name] + [arg.replace("%s", url)
                                  for arg in self.args]
         sys.audit("webbrowser.open", url)
+        self._check_url(url)
         try:
             if sys.platform[:3] == 'win':
                 p = subprocess.Popen(cmdline)
@@ -256,6 +264,7 @@ def _invoke(self, args, remote, autoraise, url=None):
 
     def open(self, url, new=0, autoraise=True):
         sys.audit("webbrowser.open", url)
+        self._check_url(url)
         if new == 0:
             action = self.remote_action
         elif new == 1:
@@ -357,6 +366,7 @@ class Konqueror(BaseBrowser):
 
     def open(self, url, new=0, autoraise=True):
         sys.audit("webbrowser.open", url)
+        self._check_url(url)
         # XXX Currently I know no way to prevent KFM from opening a new win.
         if new == 2:
             action = "newTab"
@@ -603,6 +613,7 @@ def register_standard_browsers():
     class WindowsDefault(BaseBrowser):
         def open(self, url, new=0, autoraise=True):
             sys.audit("webbrowser.open", url)
+            self._check_url(url)
             try:
                 os.startfile(url)
             except OSError:
@@ -633,6 +644,7 @@ def __init__(self, name):
 
         def open(self, url, new=0, autoraise=True):
             sys.audit("webbrowser.open", url)
+            self._check_url(url)
             assert "'" not in url
             # hack for local urls
             if not ':' in url:

Misc/NEWS.d/next/Security/2026-01-16-12-04-49.gh-issue-143930.zYC5x3.rst

@@ -0,0 +1 @@
+Reject leading dashes in URLs passed to :func:`webbrowser.open`