CVE-2021-3733

Publication date 2 September 2021

Last updated 25 August 2025

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

6.5 · Medium

Score breakdown

Description

There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.

Read the notes from the security team

Status

Package Ubuntu Release Status
python3.10 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic
Not affected
22.04 LTS jammy
Not affected
21.10 impish
Not affected
21.04 hirsute
Fixed 3.10.0~b1-3~21.04
20.04 LTS focal Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial Ignored end of standard support
14.04 LTS trusty Not in release
python3.4 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish Not in release
20.04 LTS focal Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial Not in release
14.04 LTS trusty
Fixed 3.4.3-1ubuntu1~14.04.7+esm11
python3.5 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish Not in release
21.04 hirsute Not in release
20.04 LTS focal Not in release
18.04 LTS bionic Not in release
16.04 LTS xenial
Fixed 3.5.2-2ubuntu0~16.04.13+esm1
14.04 LTS trusty
Fixed 3.5.2-2ubuntu0~16.04.4~14.04.1+esm1
python3.6 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish Not in release
21.04 hirsute Not in release
20.04 LTS focal Not in release
18.04 LTS bionic
Fixed 3.6.9-1~18.04ubuntu1.6
16.04 LTS xenial Ignored end of standard support
14.04 LTS trusty Not in release
python3.7 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish Not in release
21.04 hirsute Not in release
20.04 LTS focal Not in release
18.04 LTS bionic
Fixed 3.7.5-2ubuntu1~18.04.2
16.04 LTS xenial Ignored end of standard support
14.04 LTS trusty Not in release
python3.8 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish Not in release
21.04 hirsute Not in release
20.04 LTS focal
Fixed 3.8.10-0ubuntu1~20.04
18.04 LTS bionic
Fixed 3.8.0-3ubuntu1~18.04.2
16.04 LTS xenial Ignored end of standard support
14.04 LTS trusty Not in release
python3.9 24.10 oracular Not in release
24.04 LTS noble Not in release
23.10 mantic Not in release
23.04 lunar Not in release
22.10 kinetic Not in release
22.04 LTS jammy Not in release
21.10 impish
Not affected
21.04 hirsute
Not affected
20.04 LTS focal
Fixed 3.9.5-3~20.04.1
18.04 LTS bionic Not in release
16.04 LTS xenial Ignored end of standard support
14.04 LTS trusty Not in release

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Notes

leosilva

code affected in hirsute and devel is already patched, so both releases in python3.9 are not affected.

Severity score breakdown

Parameter Value
Base score 6.5 · Medium
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact None
Availability impact High
Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References

Related Ubuntu Security Notices (USN)

    • USN-5083-1
    • Python vulnerabilities
    • 16 September 2021
    • USN-5199-1
    • Python vulnerabilities
    • 17 December 2021
    • USN-5200-1
    • Python vulnerabilities
    • 17 December 2021

Other references