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HIGH

CVE-2021-21240

CVSS v3

7.5

HIGH

EPSS Score

3.6 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • httplib2PyPIall versions · fixed in 0.19.0

Vendor advisories

  • CVE-2021-21240 Red Hat Product Security2 products fixed · 50 known affected

    python-httplib2: Regular expression denial of service via malicious header

    python-httplib2 as a component of Red Hat Ceph Storage 2 · fence-agents-aliyun as a component of Red Hat Enterprise Linux 7 · fence-agents-all as a component of Red Hat Enterprise Linux 7

  • RHSA-2021:2116 Red Hat Product Security2 products fixed

    Red Hat Security Advisory: Red Hat OpenStack Platform 16.1.6 (python-httplib2) security update

Full record on NVD

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.

Technical details

Published
2021-02-08

Frequently asked questions

What is CVE-2021-21240?

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.

Is CVE-2021-21240 actively exploited?

Active exploitation of CVE-2021-21240 has not been confirmed. Its EPSS score was 3.6% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-21240?

CVE-2021-21240 has a CVSS v3 base score of 7.5 (HIGH severity).

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