CVE-2026-53540 | Python-Multipart: Negative Content-Length in parse_form buffers the entire body in memory

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, 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.

Published: 2026-06-22 Last update: 2026-06-26 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-53540 is rated Low Risk (19/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.22%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-53540

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-23 — 0.22% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-53540

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
3.7 3.1 LOW
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 2.2 1.4 [email protected]

Weakness enumeration for CVE-2026-53540

GitHub Security Advisory for CVE-2026-53540

GHSA-v9pg-7xvm-68hf · Severity: low · Ecosystem: pip — python-multipart: Negative Content-Length in parse_form buffers the entire body in memory

OS Trackers for CVE-2026-53540

vendor priority summary link
debian not yet assigned CVE-2026-53540 not yet assigned priority: Debian including 1 source packages (python-multipart), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 5. https://security-tracker.debian.org/tracker/CVE-2026-53540
suse low — https://www.suse.com/security/cve/CVE-2026-53540/
ubuntu medium CVE-2026-53540 medium priority: Ubuntu including 1 source packages (python-multipart), 5 status rows across 5 suites (jammy, noble, questing, resolute, upstream): needs-triage 5. https://ubuntu.com/security/CVE-2026-53540

Affected software / configurations for CVE-2026-53540

Vendor Product Version Raw CPE
fastapiexpert python-multipart < 0.0.31 cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*

References for CVE-2026-53540

cvelogic Threat Intelligence