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CVE-2021-21240

26
FAUCET Score

CVE-2021-21240 describes a Denial of Service (DoS) vulnerability in httplib2, a Python HTTP client library, affecting versions prior to 0.19.0. A malicious server can trigger a CPU burn by sending a specially crafted "www-authenticate" header containing long sequences of non-breaking space characters. This vulnerability carries a CVSS score of 7.5 (HIGH), indicating it can be exploited remotely with low complexity and no user interaction, leading to high availability impact. There is currently no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 0.19.0CPE matchmatch criteria
cpe:2.3:a:httplib2_project:httplib2:*:*:*:*:*:python:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
3.88%
Probability of exploitation in next 30 days
EPSS Percentile
89.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0388 is in the 81st percentile among its peer group of 51,506 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (7)

github_advisorypatch availablevia nvd_reference
View patch
pippatch availablevia ghsa
Product: httplib2Fixed in: 0.19.0
redhatpatch availablevia redhat_api
Product: Red Hat OpenStack Platform 16.1Fixed in: python-httplib2-0:0.13.1-2.el8ost
View patch
redhatvendor investigatingvia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: python-httplib2
redhatvendor investigatingvia redhat_api
Product: Red Hat Update Infrastructure 3 for Cloud ProvidersFixed in: python-httplib2
redhatvendor investigatingvia redhat_api
Product: Red Hat Storage 3Fixed in: python-httplib2
redhatend of lifevia redhat_api
Product: Red Hat OpenStack Platform 13 (Queens)Fixed in: python-httplib2

Vendor Advisories (2)

pipGHSA-93xj-8mrv-444mhigh

Regular Expression Denial of Service (REDoS) in httplib2

Feb 8, 2021
redhatCVE-2021-21240Low

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

Jan 9, 2021

References

github.com / httplib2/httplib2/commit/bd9ee252c8f099608019709e22c0d705e98d26bc
PatchThird Party Advisory
github.com / httplib2/httplib2/pull/182
PatchThird Party Advisory
github.com / httplib2/httplib2/security/advisories/GHSA-93xj-8mrv-444m
ExploitMitigationThird Party Advisory
pypi.org / project/httplib2
ProductThird Party Advisory