A Python security update has been released for Ubuntu 18.04 LTS.

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Ubuntu Security Notice USN-5200-1
December 17, 2021

python3.7, python3.8 vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS

Summary:

Python could be made to crash if it receives specially crafted input
from a malicious server.

Software Description:
- python3.7: An interactive high-level object-oriented language
- python3.8: An interactive high-level object-oriented language

Details:

It was discovered that the urllib.request.AbstractBasicAuthHandler class
in Python contains regex allowing for catastrophic backtracking. Specially
crafted traffic from a malicious HTTP server could cause a regular
expression
denial of service (ReDoS) condition for a client.
(CVE-2020-8492)

It was discovered that the urllib.request.AbstractBasicAuthHandler class
in Python contains regex with a quadratic worst-case time complexity.
Specially crafted traffic from a malicious HTTP server could cause a
regular
expression denial of service (ReDoS) condition for a client.
(CVE-2021-3733)

It was discovered that the Python urllib http client could enter into an
infinite
loop when incorrectly handling certain server responses (100 Continue
response).
Specially crafted traffic from a malicious HTTP server could cause a
denial of
service (DoS) condition for a client.
(CVE-2021-3737)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS:
  libpython3.7-stdlib             3.7.5-2ubuntu1~18.04.2
  libpython3.8-stdlib             3.8.0-3ubuntu1~18.04.2
  python3.7                          3.7.5-2ubuntu1~18.04.2
  python3.7-minimal             3.7.5-2ubuntu1~18.04.2
  python3.8                          3.8.0-3ubuntu1~18.04.2
  python3.8-minimal             3.8.0-3ubuntu1~18.04.2

In general, a standard system update will make all the necessary changes.

References:
    https://ubuntu.com/security/notices/USN-5200-1
  CVE-2020-8492, CVE-2021-3733, CVE-2021-3737

Package Information:
    https://launchpad.net/ubuntu/+source/python3.7/3.7.5-2ubuntu1~18.04.2
    https://launchpad.net/ubuntu/+source/python3.8/3.8.0-3ubuntu1~18.04.2