High severity · published Jun 22, 2026
CVE-2026-54283
Starlette: request.form() limits silently ignored for application/x-www-form-urlencoded enable DoS
7.5
CVSS
0.5%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 41% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ST
starlette · Kludex
>= 0.4.1, < 1.3.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-54283
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-54283
Mitigation
https://github.com/Kludex/starlette/security/advisories/GHSA-82w8-qh3p-5jfq
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