CVE-2021-21240

Name: CVE-2021-21240
Creator: NVD / NIST
Published: 2021-02-08T20:15:12.197+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 3.88%

Last modified Jun 17, 2026

CVE-2021-21240 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. EPSS estimates a 3.88% chance of exploitation in the next 30 days.

Description

httplib2 is a comprehensive HTTP client library for Python. In httplib2 before version 0.19.0, a malicious server which responds with long series of "\xa0" characters in the "www-authenticate" header may cause Denial of Service (CPU burn while parsing header) of the httplib2 client accessing said server. This is fixed in version 0.19.0 which contains a new implementation of auth headers parsing using the pyparsing library.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

3.88%

88.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Httplib2 Project	Httplib2	< 0.19.0

References

https://github.com/httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bcPatch, Third Party Advisory
https://github.com/httplib2/httplib2/pull/182Patch, Third Party Advisory
https://github.com/httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444mExploit, Mitigation, Third Party Advisory
https://pypi.org/project/httplib2Product, Third Party Advisory
https://github.com/httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bcPatch, Third Party Advisory
https://github.com/httplib2/httplib2/pull/182Patch, Third Party Advisory
https://github.com/httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444mExploit, Mitigation, Third Party Advisory
https://pypi.org/project/httplib2Product, Third Party Advisory

Timeline

Published: Feb 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21240?

How severe is CVE-2021-21240?

CVE-2021-21240 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 3.88% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21240?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21240?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST