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CVE Record

CVE-2021-28861: Python 3.x through 3.10 has an open redirection vulnerability in lib/http/server.py due to no protection ag...

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."

MediumCVSS 6.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-28861 concerns Python's built-in http.server handling of paths that begin with multiple slashes. A crafted link could cause an open redirect and possible information disclosure. The issue is medium severity, disputed in part because Python documents http.server as unsuitable for production use.

Executive priority

Handle as a targeted hygiene issue, not an emergency. Prioritize internet-facing or business-facing uses first, then developer and lab environments. The main business risk is avoidable exposure from using a non-production Python module in places where users or external traffic can reach it.

Technical view

The reported weakness is CWE-601 in lib/http/server.py for Python 3.x through 3.10. The CVSS vector indicates network reachability, low attack complexity, no privileges, required user interaction, and high confidentiality impact. Public references include Python bug and pull request discussions plus Linux distribution advisories.

Likely exposure

Most exposure is likely where Python http.server is reachable by users, automation, or the internet. Production systems should not depend on it. Developer workstations, temporary file servers, lab environments, containers, and packaged Python runtimes may still carry the affected code path.

Exploitation context

The provided bundle does not show CISA KEV listing or active exploitation. Exploitation depends on user interaction and a reachable http.server instance. The CVE is also disputed because the module is explicitly documented as offering only basic security checks, not production-grade protections.

Researcher notes

Evidence supports an open redirect class issue in Python http.server with confidentiality impact, but affected product metadata is sparse and the record notes dispute. Avoid broad claims beyond Python 3.x through 3.10 and referenced distribution advisories unless confirmed from vendor-specific package data.

Mitigation direction

  • Do not expose Python http.server as a production or internet-facing service.
  • Update Python packages using Python or operating system vendor guidance.
  • Review Fedora, Gentoo, Debian, and platform advisories for corrected package status.
  • Replace http.server with a production web server for real workloads.
  • Use edge validation as a compensating control only after vendor review.

Validation and detection

  • Inventory systems, containers, scripts, and tools using Python http.server.
  • Identify Python 3.x through 3.10 runtimes and distribution package versions.
  • Confirm whether any http.server instance is reachable from untrusted networks.
  • Review access logs for URI paths beginning with repeated slashes.
  • Check whether vendor advisories mark the installed package as fixed.
Prepared
Confidence
medium
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-601: User-session and phishing behavior lookup

Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-28861 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
21Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.5CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N2.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.5Medium
CVSS 3.1 vector shape for CVE-2021-28861Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

CWE-601

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-601 · source CWE mapping

URL Redirection to Untrusted Site ('Open Redirect')

URL Redirection to Untrusted Site ('Open Redirect') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs