Debian Security Advisory

DLA-2619-1 python3.5 -- LTS security update

Date Reported:
05 Apr 2021
Affected Packages:
Security database references:
In Mitre's CVE dictionary: CVE-2021-3177, CVE-2021-3426, CVE-2021-23336.
More information:

Three security issues have been discovered in python3.5:

  • CVE-2021-3177

    Python 3.x has a buffer overflow in PyCArg_repr in _ctypes/callproc.c, which may lead to remote code execution in certain Python applications that accept floating-point numbers as untrusted input. This occurs because sprintf is used unsafely.

  • CVE-2021-3426

    Running `pydoc -p` allows other local users to extract arbitrary files. The `/getfile?key=path` URL allows to read arbitrary file on the filesystem.

    The fix removes the getfile feature of the pydoc module which could be abused to read arbitrary files on the disk (directory traversal vulnerability).

  • CVE-2021-23336

    The Python3.5 vulnerable to Web Cache Poisoning via urllib.parse.parse_qsl and urllib.parse.parse_qs by using a vector called parameter cloaking. When the attacker can separate query parameters using a semicolon (;), they can cause a difference in the interpretation of the request between the proxy (running with default configuration) and the server. This can result in malicious requests being cached as completely safe ones, as the proxy would usually not see the semicolon as a separator, and therefore would not include it in a cache key of an unkeyed parameter.

    Attention, API-change!

    Please be sure your software is working properly if it uses `urllib.parse.parse_qs` or `urllib.parse.parse_qsl`, `cgi.parse` or `cgi.parse_multipart`.

    Earlier Python versions allowed using both ``;`` and ``&`` as query parameter separators in `urllib.parse.parse_qs` and `urllib.parse.parse_qsl`. Due to security concerns, and to conform with newer W3C recommendations, this has been changed to allow only a single separator key, with ``&`` as the default. This change also affects `cgi.parse` and `cgi.parse_multipart` as they use the affected functions internally. For more details, please see their respective documentation.

    For Debian 9 stretch, these problems have been fixed in version 3.5.3-1+deb9u4.

    We recommend that you upgrade your python3.5 packages.

    For the detailed security status of python3.5 please refer to its security tracker page at:

    Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: