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Debian LinuxOperating system · Debian

CVE-2020-25032

HIGH · 7.5 CVSS v3.1 Published 2020-08-31
Fix available
A fix is available. Upgrade to 3.0.9 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An issue was discovered in Flask-CORS (aka CORS Middleware for Flask) before 3.0.9. It allows ../ directory traversal to access private resources because resource matching does not ensure that pathnames are in a canonical format.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Flask-CORS before version 3.0.9 contains a path traversal vulnerability in its resource matching logic. The library fails to canonicalize pathnames before matching, allowing attackers to use '../' sequences to access private resources outside the intended web root or protected directories.

MitigationUpgrade Flask-CORS to version 3.0.9 or later, which implements proper path canonicalization to prevent directory traversal attacks.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Debian LinuxOperating system
Affected:= 10.0
Flask CorsApplication
Affected:< 3.0.9
Backports SleApplication
Affected:= 15.0
LeapOperating system
Affected:= 15.1= 15.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check Flask-CORS package version
    Run 'pip show flask-cors' or inspect your installed packages to find the version of Flask-CORS
    Affected if Version is below 3.0.9
  2. Identify CORS resource configuration
    Search Flask application code for CORS initialization using the resources parameter, such as CORS(app, resources={...}) or @cross_origin() decorators with specific resource path patterns
    Affected if CORS is configured with path-based resource restrictions
  3. Examine path handling before CORS matching
    Review how request paths are processed in your application - verify whether paths are normalized using os.path.realpath() or os.path.abspath() before being evaluated against CORS resource rules
    Affected if Paths are matched against CORS resource rules without canonicalization, allowing '../' sequences to bypass restrictions

Your environment is affected if Flask-CORS version is below 3.0.9 AND CORS resource path matching is in use without path canonicalization.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 3.0.9 or later
Fixed in 3.0.9
Interim mitigation

Upgrade Flask-CORS to version 3.0.9 or later, which implements proper path canonicalization to prevent directory traversal attacks.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-25032 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data