CVE-2026-53538Network attack vector

Parameter smuggling via semicolon separator mismatch

Published Jun 22, 2026 · Updated Jun 22, 2026

Parameter smuggling in Kludex python-multipart before 0.0.30 allows remote attackers to inject hidden form fields via semicolons. QuerystringParser's FIELD_NAME and FIELD_DATA states treat a semicolon as a boundary after searching for an ampersand, unlike compliant intermediaries. Exploitation requires an ampersand-only upstream inspector and a backend that assigns security significance to the resulting extra or overriding field.

CVSS severity3.7
Low
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Parameter smuggling in Kludex python-multipart before 0.0.30 allows remote attackers to inject hidden form fields via semicolons. QuerystringParser's FIELD_NAME and FIELD_DATA states treat a semicolon as a boundary after searching for an ampersand, unlike compliant intermediaries. Exploitation requires an ampersand-only upstream inspector and a backend that assigns security significance to the resulting extra or overriding field.

The record

CVE
CVE-2026-53538
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
Kludex
Product
python-multipart
Classifications
CWE-436, CWE-444, T1190
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=< 0.0.30

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Kludex · python-multipartversion=< 0.0.30

Published CVSS scores

3.7GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

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.

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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-436Interpretation Conflict
CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
T1190Exploit Public-Facing Application

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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