CVE-2026-54283Network attack vector

Denial of service via unenforced urlencoded limits

Published Jun 22, 2026 · Updated Jun 22, 2026

Denial of service in Starlette 0.4.1 through 1.3.0 allows remote attackers to exhaust CPU and memory via urlencoded form bodies. The urlencoded parser appends every field without a count check and accumulates each field name and value without a size check, ignoring configured max_fields and max_part_size limits. Applications are exposed only when an endpoint calls request.form() for application/x-www-form-urlencoded; crafted bodies can block the event loop or force memory allocation until service is unavailable.

CVSS severity7.5
High
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Starlette 0.4.1 through 1.3.0 allows remote attackers to exhaust CPU and memory via urlencoded form bodies. The urlencoded parser appends every field without a count check and accumulates each field name and value without a size check, ignoring configured max_fields and max_part_size limits. Applications are exposed only when an endpoint calls request.form() for application/x-www-form-urlencoded; crafted bodies can block the event loop or force memory allocation until service is unavailable.

The record

CVE
CVE-2026-54283
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
Kludex
Product
Starlette
Classifications
CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.4.1, < 1.3.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Kludex · Starletteversion=>= 0.4.1, < 1.3.1

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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