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

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Ubuntu Security Notice USN-5199-1
December 17, 2021

python3.6 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:
- python3.6: An interactive high-level object-oriented language

Details:

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:
libpython3.6-stdlib 3.6.9-1~18.04ubuntu1.6
python3.6 3.6.9-1~18.04ubuntu1.6
python3.6-minimal 3.6.9-1~18.04ubuntu1.6

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

References:
  https://ubuntu.com/security/notices/USN-5199-1
CVE-2021-3733, CVE-2021-3737

Package Information:
  https://launchpad.net/ubuntu/+source/python3.6/3.6.9-1~18.04ubuntu1.6