CVE-2026-40347 | Python-Multipart affected by Denial of Service via large multipart preamble or epilogue data

Python-Multipart is a streaming multipart parser for Python. Versions prior to 0.0.26 have a denial of service vulnerability when parsing crafted `multipart/form-data` requests with large preamble or epilogue sections. Upgrade to version 0.0.26 or later, which skips ahead to the next boundary candidate when processing leading CR/LF data and immediately discards epilogue data after the closing boundary.

Published: 2026-04-17 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40347 is rated Low Risk (30.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.35%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

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-2026-40347

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 2026-06-15 0.04% 0.35% +0.31%
2 2026-04-18 — 0.04% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40347

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/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:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
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.
 3.9 1.4 [email protected]

Weakness enumeration for CVE-2026-40347

GitHub Security Advisory for CVE-2026-40347

GHSA-mj87-hwqh-73pj · Severity: medium · Ecosystem: pip — python-multipart affected by Denial of Service via large multipart preamble or epilogue data

OS Trackers for CVE-2026-40347

vendor priority summary link
debian not yet assigned CVE-2026-40347 not yet assigned priority: Debian including 1 source packages (python-multipart), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 3, resolved 2. https://security-tracker.debian.org/tracker/CVE-2026-40347
suse medium CVE-2026-40347 severity moderate: SUSE including 3 source package names (python311-python-multipart-0.0.26-1.1, python313-python-multipart-0.0.26-1.1, python314-python-multipart-0.0.26-1.1), 3 product×package rows across 1 product lines (openSUSE Tumbleweed): Fixed 3. https://www.suse.com/security/cve/CVE-2026-40347/
ubuntu medium CVE-2026-40347 medium priority: Ubuntu including 1 source packages (python-multipart), 5 status rows across 5 suites (jammy, noble, questing, resolute, upstream): needs-triage 4, released 1. https://ubuntu.com/security/CVE-2026-40347

Affected software / configurations for CVE-2026-40347

Vendor Product Version Raw CPE
fastapiexpert python-multipart < 0.0.26 cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*

References for CVE-2026-40347

cvelogic Threat Intelligence