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CVE-2021-33503

25
FAUCET Score

CVE-2021-33503 is a denial-of-service vulnerability in urllib3 versions prior to 1.26.5, affecting products like fedoraproject, oracle, and python. This flaw arises from catastrophic backtracking in the authority regular expression when processing URLs with numerous '@' characters, leading to a system crash if such a URL is provided. Rated 7.5 HIGH, it requires no user interaction and can be exploited remotely with low attack complexity, resulting in high availability impact. Currently, there is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
>= 1.25.4, < 1.26.5CPE matchmatch criteria
cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*
33CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
34CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
12.4.0.0CPE matchmatch criteria
cpe:2.3:a:oracle:enterprise_manager_ops_center:12.4.0.0:*:*:*:*:*:*:*
17.1CPE matchmatch criteria
cpe:2.3:a:oracle:instantis_enterprisetrack:17.1:*:*:*:*:*:*:*

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
3.25%
Probability of exploitation in next 30 days
EPSS Percentile
87.0%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0325 is in the 77th percentile among its peer group of 51,485 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 (49)

github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: CBL Mariner 2.0 ARMFixed in: 1.25.9-3
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 ARMFixed in: 1.25.9-2
microsoftpatch availablevia msrc
Product: CBL Mariner 2.0 x64Fixed in: 1.25.9-3
microsoftpatch availablevia msrc
Product: 16991-16820Fixed in: 1.25.9-2
microsoftpatch availablevia msrc
Product: 19036-16823Fixed in: 1.25.9-3
microsoftpatch availablevia msrc
Product: cbl2 python-urllib3 1.25.9-3 on CBL Mariner 2.0Fixed in: 1.25.9-3
microsoftpatch availablevia msrc
Product: cm1 python-urllib3 1.25.9-2 on CBL Mariner 1.0Fixed in: 1.25.9-2
microsoftpatch availablevia msrc
Product: CBL Mariner 1.0 x64Fixed in: 1.25.9-2
oraclepatch availablevia nvd_reference
View patch
pippatch availablevia ghsa
Product: urllib3Fixed in: 1.26.5
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-click-0:7.1.2-3.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-gnupg-0:0.4.6-3.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-jinja2-0:2.11.2-3.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-markupsafe-0:1.1.1-4.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python3-semantic-version-0:2.8.5-3.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-galaxy-ng-0:4.2.6-1.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: python-urllib3-0:1.26.5-1.el8pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: python39:3.9-8050020210811100211.d428a79b
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: python39-devel:3.9-8050020210811100211.d428a79b
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: python38:3.8-8050020210811101222.e3d35cca
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 8Fixed in: python38-devel:3.8-8050020210811101222.e3d35cca
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Satellite 6.10 for RHEL 7Fixed in: python-urllib3-0:1.26.5-1.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-babel-0:2.7.0-12.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-0:3.8.11-2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-cryptography-0:2.8-5.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-jinja2-0:2.10.3-6.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-lxml-0:4.4.1-7.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-pip-0:19.3.1-2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-python38-python-urllib3-0:1.25.7-7.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-babel-0:2.7.0-12.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-0:3.8.11-2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-jinja2-0:2.10.3-6.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-lxml-0:4.4.1-7.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-pip-0:19.3.1-2.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-urllib3-0:1.25.7-7.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.7 EUSFixed in: rh-python38-python-cryptography-0:2.8-5.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: automation-hub-0:4.2.6-1.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-chardet-0:3.0.4-3.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-click-0:7.1.2-3.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-gnupg-0:0.4.6-3.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-jinja2-0:2.11.2-3.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-markupsafe-0:1.1.1-4.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python3-semantic-version-0:2.8.5-3.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-galaxy-ng-0:4.2.6-1.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 7Fixed in: python-urllib3-0:1.26.5-1.el7pc
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Automation Hub 4.2 for RHEL 8Fixed in: automation-hub-0:4.2.6-1.el8pc
View patch
redhatvendor investigatingvia redhat_api
Product: Red Hat 3scale API Management Platform 2Fixed in: system
redhatno patchvia redhat_api
Product: Red Hat Quay 3Fixed in: quay/quay-rhel8

Vendor Advisories (4)

microsoft2021-Jul/CVE-2021-33503

CVE-2021-33503

Jul 13, 2021
microsoft2021-Jun/CVE-2021-33503Important

An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component the authority regular expression exhibits catastrophic backtracking causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.

Jun 8, 2021
pipGHSA-q2q7-5pp4-w6pghigh

Catastrophic backtracking in URL authority parser when passed URL containing many @ characters

Jun 1, 2021
redhatCVE-2021-33503Moderate

python-urllib3: ReDoS in the parsing of authority part of URL

Jun 1, 2021

References

github.com / advisories/GHSA-q2q7-5pp4-w6pg
Third Party Advisory
github.com / urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec
PatchThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73
security.gentoo.org / glsa/202107-36
Third Party Advisory
oracle.com / security-alerts/cpuoct2021.html
PatchThird Party Advisory