Affected versions of the Mako package are vulnerable to Path Traversal due to a mismatch between the posixpath-based URI normalisation used in TemplateLookup.get_template() and the Windows-native ntpath path resolution used by os.path.isfile() and os.path.normpath() in Template.__init__(). The get_template() method normalises the URI using posixpath, which treats backslashes as literal characters and thus fails to detect directory traversal sequences embedded via backslash separators, while os.path.normpath() in Template.__init__() resolves backslash-based .. sequences to a form that bypasses the startswith("..") guard. An attacker who can supply a user-controlled template name or include path to TemplateLookup.get_template() on a Windows host can read arbitrary files outside the configured template directory, and if the targeted file contains Mako or Python template syntax, it may additionally be parsed and executed as a template.

Affected versions of the Mako package are vulnerable to Path Traversal due to inconsistent stripping of leading slashes between TemplateLookup.get_template() and Template.init when resolving a template URI. TemplateLookup.get_template() strips all leading forward slashes before joining the URI with the template directory via posixpath.join, while Template.init strips only a single leading slash before calling normpath, so a URI beginning with a double slash is resolved to an absolute path like /etc/passwd that bypasses the subsequent startswith traversal check. An attacker who can pass untrusted input to TemplateLookup.get_template() can exploit this to read arbitrary files readable by the process and have their contents returned as rendered template output, resulting in unauthorized arbitrary file disclosure.

Mako before 1.2.2 is vulnerable to Regular expression Denial of Service when using the Lexer class to parse. This also affects babelplugin and linguaplugin.
https://pyup.io/posts/pyup-discovers-redos-vulnerabilities-in-top-python-packages

Affected versions of the Mako package are vulnerable to Path Traversal due to a mismatch between the posixpath-based URI normalisation used in TemplateLookup.get_template() and the Windows-native ntpath path resolution used by os.path.isfile() and os.path.normpath() in Template.__init__(). The get_template() method normalises the URI using posixpath, which treats backslashes as literal characters and thus fails to detect directory traversal sequences embedded via backslash separators, while os.path.normpath() in Template.__init__() resolves backslash-based .. sequences to a form that bypasses the startswith("..") guard. An attacker who can supply a user-controlled template name or include path to TemplateLookup.get_template() on a Windows host can read arbitrary files outside the configured template directory, and if the targeted file contains Mako or Python template syntax, it may additionally be parsed and executed as a template.

Affected versions of the Mako package are vulnerable to Path Traversal due to inconsistent stripping of leading slashes between TemplateLookup.get_template() and Template.init when resolving a template URI. TemplateLookup.get_template() strips all leading forward slashes before joining the URI with the template directory via posixpath.join, while Template.init strips only a single leading slash before calling normpath, so a URI beginning with a double slash is resolved to an absolute path like /etc/passwd that bypasses the subsequent startswith traversal check. An attacker who can pass untrusted input to TemplateLookup.get_template() can exploit this to read arbitrary files readable by the process and have their contents returned as rendered template output, resulting in unauthorized arbitrary file disclosure.

Mako before 1.2.2 is vulnerable to Regular expression Denial of Service when using the Lexer class to parse. This also affects babelplugin and linguaplugin.
https://pyup.io/posts/pyup-discovers-redos-vulnerabilities-in-top-python-packages