6.5

CVE-2021-28363: fedoraproject fedora Improper Certificate Validation

Modified
AliasesALPINE-CVE-2021-28363GHSA-5phf-pp7p-vc2rPYSEC-2021-59
Published 15-03-2021Last modified 14-10-2026

Vulnerability summary

CVE-2021-28363 is a medium (CVSS 6.5) Improper Certificate Validation vulnerability in fedoraproject fedora. EPSS estimates a 2.17% chance of exploitation in the next 30 days, higher than 82.2% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 6.5, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
6.5/10
010
Medium · v3.1 (NVD)
EPSS score
2.17%
0%100%
Low · +0.06 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2
MGASA-2021-0371MGASA-2021-0377

Timeline

  1. 15-03-2021
    PublishedVulnerability first disclosed.
  2. 14-10-2026
    Last modifiedVulnerability information updated.

Description

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

CVSS metrics

7 scores · 5 sources · 3 versions

EPSS trend

Probability

2.17%

Chance of exploitation in the next 30 days

Percentile

82%

Versus all other CVEs

30-day change

Increase +0.06 pp

From 2.11% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Redhat2 products
  • python-urllib3< 1:1.24.3-2.el7
  • python2-urllib3< 1:1.24.3-2.el7
Alpine1 product
  • py3-urllib3< 1.26.4-r0
Debian1 product
  • python-urllib3< 1.26.4-1
Fedoraproject1 product
Oracle1 product
PyPI1 product
  • urllib3< 8d65ea1ecf6e2cdc27d42124e587c1b83a3118b0 | ≥ 1.26.0, < 1.26.4
Python1 product

7 vendors · 8 products

References

30 links
Show all 30 references