CVE-2021-28861
HIGHEPSS 86th pctlDescription
Python 3.x through 3.10 has an open redirection vulnerability in lib/http/server.py due to no protection against multiple (/) at the beginning of URI path which may leads to information disclosure. NOTE: this is disputed by a third party because the http.server.html documentation page states "Warning: http.server is not recommended for production. It only implements basic security checks."
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
Exploit Intelligence
Elevated risk: more likely to be exploited than 86% of all known CVEs.
References
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- security.gentoo.org
- lists.debian.org
- lists.debian.org
- cert-portal.siemens.com
Related Vulnerabilities
Other CWE-601 (Open Redirect) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2018-11784 | Medium | 4.3 | 98% | - | Fix |
| CVE-2025-4123 | High | 7.6 | 97% | - | Fix |
| CVE-2021-22881 | Medium | 6.1 | 87% | - | Fix |
| CVE-2022-45402 | Medium | 6.1 | 82% | - | Fix |
| CVE-2017-1000117 | High | 8.8 | 78% | - | Fix |
| CVE-2019-10098 | Medium | 6.1 | 74% | - | Fix |
Common questions
How do I fix CVE-2021-28861?
Published advisories record a fix for 379 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-28861 being actively exploited?
Not that we know of. CVE-2021-28861 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 2.7% is the estimated probability that it will be exploited in the next 30 days. That is higher than 86% of all scored CVEs.
How severe is CVE-2021-28861?
CVE-2021-28861 has a CVSS v3 base score of 7.4, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-28861 affect?
Published advisories record a fix for pypy3 (Debian), python3.11 (Debian), Cython (Red Hat / RHEL), Cython (Rocky), and 375 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-10-14.