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StarletteApplication · Encode

CVE-2026-54283

HIGH · 7.5 CVSS v3.1 Published 2026-06-22
Fix available
A fix is available. Upgrade to 1.3.1 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
Starlette is a lightweight ASGI framework/toolkit. From 0.4.1 until 1.3.1, request.form() accepts max_fields and max_part_size to bound resource consumption while parsing form data. These limits are enforced for multipart/form-data, but silently ignored for application/x-www-form-urlencoded. An unauthenticated attacker can therefore send a urlencoded body with an arbitrarily large number of fields or an arbitrarily large field, even when the application configured limits it believed would apply. This vulnerability is fixed in 1.3.1.

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

In Starlette versions 0.4.1 through 1.3.0, the request.form() method enforces max_fields and max_part_size limits only for multipart/form-data requests, while silently ignoring them for application/x-www-form-urlencoded requests. This allows unauthenticated attackers to send urlencoded bodies with arbitrarily large numbers of fields or arbitrarily large individual fields, causing resource exhaustion.

MitigationUpgrade Starlette to version 1.3.1 or later to enforce the configured limits on application/x-www-form-urlencoded requests.

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
StarletteApplication
Affected:>= 0.4.1, < 1.3.1

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
None
Integrity
None
Availability
High

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

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 Starlette version
    Run 'pip show starlette' or check your requirements file to find the installed version of Starlette
    Affected if Version is >= 0.4.1 and < 1.3.1
  2. Identify form() usage in code
    Search your codebase for 'request.form()' or '.form()' method calls within Starlette request handlers
    Affected if The application uses the form() method to parse request bodies
  3. Check accepted content types
    Inspect your Starlette routes and middleware to determine if application/x-www-form-urlencoded requests are accepted
    Affected if Your application accepts application/x-www-form-urlencoded content type requests that use form()
  4. Verify max_fields or max_part_size configuration
    Search for form(max_fields= or form(max_part_size= configurations in your code
    Affected if You rely on max_fields or max_part_size limits to constrain request sizes but accept urlencoded requests

You are affected if you use Starlette >= 0.4.1 and < 1.3.1, your application accepts application/x-www-form-urlencoded requests, and those requests are processed using the form() method without proper limits enforced.

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.

dbcve · scoped
Upgrade available Upgrade to 1.3.1 or later
Fixed in 1.3.1
Interim mitigation

Upgrade Starlette to version 1.3.1 or later to enforce the configured limits on application/x-www-form-urlencoded requests.

Recommended fix High confidence

1.3.1

  1. Upgrade Starlette to version 1.3.1 or later by running: pip install starlette>=1.3.1
  2. After upgrading, verify the application still functions correctly by testing form handling functionality
  3. If using a dependency manager (like poetry or pip-tools), update the locked dependency version to ensure the upgrade is applied in deployment
Caveat No breaking changes specifically mentioned in the provided description; this is a security-focused patch release

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Starlette Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,340
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,144.

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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-2026-54283 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