Cyber Resilience

CVE-2026-53540

Fastapiexpert Python-Multipart ≤ 0.0.31

Published
22 June 2026
Modified
26 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 3.7
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS Score 0.0022 12th percentile
Risk Priority 31 floored blend · peak EPSS

Summary

CVE-2026-53540 is a low-severity Improper Validation of Specified Quantity in Input (CWE-1284) vulnerability in Fastapiexpert Python-Multipart. Its CVSS base score is 3.7 (Low).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 12th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.31, parse_form() did not validate the Content-Length header before using it to bound its chunked read of the request body. A negative Content-Length turned the bounded read into a read-until-EOF,…

more

so the entire body was loaded into memory in a single read instead of in fixed-size chunks. This vulnerability is fixed in 0.0.31.

CWE(s)
CWE-1284

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
T1499 Endpoint Denial of Service Impact
Adversaries may perform Endpoint Denial of Service (DoS) attacks to degrade or block the availability of services to users.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-53537Same product: Fastapiexpert Python-Multipart
CVE-2026-24486Same product: Fastapiexpert Python-Multipart
CVE-2026-53538Same product: Fastapiexpert Python-Multipart
CVE-2026-53539Same product: Fastapiexpert Python-Multipart
CVE-2026-40347Same product: Fastapiexpert Python-Multipart
CVE-2024-8558Shared CWE-1284
CVE-2023-27941Shared CWE-1284
CVE-2025-8320Shared CWE-1284
CVE-2025-14689Shared CWE-1284
CVE-2026-2403Shared CWE-1284

Affected Assets

fastapiexpert
python-multipart
≤ 0.0.31

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V6.7.2
  • V1.4.2
  • V2.1.1
  • V2.2.1

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

SI-10 requires validity checks on information inputs, directly stopping acceptance of malformed quantities before they can be used.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require proper quantity/length validation in input handling.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development can detect missing quantity validation but does not itself implement the control.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates input validation for quantity fields, directly preventing CWE-1284.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for validation of size/length inputs, mitigating CWE-1284.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles encourage robust input handling but do not specifically address quantity validation.

A.8.28 Secure coding partial match
prevents

Secure coding standards require explicit checks on numeric quantity inputs, fully addressing CWE-1284.

References