HTML-escape the plain traceback in cgitb's HTML output, to prevent

the traceback inadvertently or maliciously closing the comment and
injecting HTML into the error page.

Lib/cgitb.py

@@ -183,7 +183,8 @@ function calls leading up to the error, in the order they occurred.</p>'''
 
 %s
 -->
-''' % ''.join(traceback.format_exception(etype, evalue, etb))
+''' % pydoc.html.escape(
+          ''.join(traceback.format_exception(etype, evalue, etb)))
 
 def text((etype, evalue, etb), context=5):
     """Return a plain text document describing a given traceback."""

Misc/NEWS

@@ -207,6 +207,10 @@ Core and builtins
 Library
 -------
 
+- HTML-escape the plain traceback in cgitb's HTML output, to prevent
+  the traceback inadvertently or maliciously closing the comment and
+  injecting HTML into the error page.
+
 - The popen2 module and os.popen* are deprecated.  Use the subprocess module.
 
 - Added an optional credentials argument to SMTPHandler, for use with SMTP