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CVE-2021-28363

23
FAUCET Score

CVE-2021-28363 is a medium-severity vulnerability affecting urllib3 library versions 1.26.x before 1.26.4, as well as various Fedora and Oracle products utilizing it. The flaw involves a critical omission of SSL certificate hostname validation when connecting to HTTPS proxies, potentially allowing an attacker to intercept or redirect traffic if a valid, but incorrect, certificate is presented. With a CVSS score of 6.5, this network-based vulnerability requires no user interaction and could lead to low confidentiality and integrity impacts. 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
>= 1.26.0, < 1.26.4CPE matchmatch criteria
cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*
34CPE matchmatch criteria
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
8.59CPE matchmatch criteria
cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.59:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.5MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
2.5
CvssVersion
3.1

Exploit Intelligence

EPSS Score
2.11%
Probability of exploitation in next 30 days
EPSS Percentile
79.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0211 is in the 69th percentile among its peer group of 23,705 CVEs.

Social Chatter

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

Media Mentions

No media coverage found for this CVE.

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

Remediation

Patch Available

Vendor Patches (4)

github_advisorypatch availablevia nvd_reference
View patch
oraclepatch availablevia nvd_reference
View patch
pippatch availablevia ghsa
Product: urllib3Fixed in: 1.26.4
redhatpatch availablevia redhat_api
Product: Red Hat OpenShift Container Platform 3.11Fixed in: python-urllib3-1:1.24.3-2.el7
View patch

Vendor Advisories (2)

pipGHSA-5phf-pp7p-vc2rmedium

Using default SSLContext for HTTPS requests in an HTTPS proxy doesn't verify certificate hostname for proxy connection

Mar 19, 2021
redhatCVE-2021-28363Moderate

python-urllib3: HTTPS proxy host name not validated when using default SSLContext

Mar 15, 2021

References

github.com / urllib3/urllib3/commit/8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0
PatchThird Party Advisory
github.com / urllib3/urllib3/commits/main
PatchThird Party Advisory
github.com / urllib3/urllib3/security/advisories/GHSA-5phf-pp7p-vc2r
MitigationThird Party Advisory
lists.fedoraproject.org / archives/list/package-announce%40lists.fedoraproject.org/message/4S65ZQVZ2ODGB52IC7VJDBUK4M5INCXL
pypi.org / project/urllib3/1.26.4
Third Party Advisory
security.gentoo.org / glsa/202107-36
Third Party Advisory
security.gentoo.org / glsa/202305-02
security.netapp.com / advisory/ntap-20240621-0007
oracle.com / security-alerts/cpuoct2021.html
PatchThird Party Advisory