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CVE Record

CVE-2021-23385: Open Redirect

This affects all versions of package Flask-Security. When using the get_post_logout_redirect and get_post_login_redirect functions, it is possible to bypass URL validation and redirect a user to an arbitrary URL by providing multiple back slashes such as \\\evil.com/path. This vulnerability is only exploitable if an alternative WSGI server other than Werkzeug is used, or the default behaviour of Werkzeug is modified using 'autocorrect_location_header=False. **Note:** Flask-Security is not maintained anymore.

MediumCVSS 5.4Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-23385 is an open redirect issue in Flask-Security. A user can be sent from a trusted application to an attacker-controlled site after login or logout. Business risk is mainly phishing, credential harvesting, and trust abuse, not direct server takeover.

Executive priority

Treat as a targeted web trust and phishing risk. Prioritize internet-facing applications with Flask-Security authentication flows, but rank below remote code execution or unauthenticated data exposure issues.

Technical view

Flask-Security redirect validation in get_post_logout_redirect and get_post_login_redirect can be bypassed with URLs containing multiple backslashes. The issue is exploitable only with a non-Werkzeug WSGI server or modified Werkzeug behavior using autocorrect_location_header=False. Sources state Flask-Security is no longer maintained.

Likely exposure

Exposure is limited to Python web applications using Flask-Security login or logout redirects, especially deployments not using default Werkzeug redirect handling. Debian-packaged Flask-Security users should verify distribution security updates.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. Exploitation requires user interaction and a specific server/configuration condition, but the attack can support phishing by abusing trusted application URLs.

Researcher notes

Key uncertainty is deployment context. The CVE affects Flask-Security broadly, but practical exploitability depends on WSGI behavior or changed Werkzeug defaults. No upstream maintenance status suggests remediation may require distribution patches or replacement, not only a version bump.

Mitigation direction

  • Inventory applications and packages for Flask-Security usage.
  • Check whether login or logout post-redirect helpers are used.
  • Apply relevant vendor or distribution security guidance, including Debian updates where applicable.
  • Review Werkzeug and WSGI redirect handling configuration.
  • Plan migration away from unmaintained Flask-Security where feasible.

Validation and detection

  • Confirm whether Flask-Security is present in dependency manifests or runtime environments.
  • Identify calls to get_post_login_redirect and get_post_logout_redirect.
  • Review WSGI server choice and Werkzeug autocorrect_location_header settings.
  • Test that login and logout redirects reject external destinations.
  • Check Debian package status if using distribution-managed Flask-Security.
Prepared
Confidence
high
Sources
6

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

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CVE-2021-23385 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.4 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P/RL:U/RC:C

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
5Source 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
5.4CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P/RL:U/RC:C2.82.5Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.4Medium
CVSS 3.1 vector shape for CVE-2021-23385Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P/RL:U/RC:C

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/aFlask-Security0Listed
Weakness

CWE details

No CWE listed

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