CVE-2026-40347

MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under NVD CVSS v3. EPSS exploit probability: 0.4%, top 72% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
5.3
EG Score
5.3(medium)
EG Risk
39(Track)
EG Risk 39/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
28%
KEV
Not listed

Published

April 18, 2026

Last Modified

April 24, 2026

Advisory Details (2)

Auto-updated Aug 3, 2026
Patch available. Sources: github_release, github.
github Patch Available

Denial of Service via large multipart preamble or epilogue data · Advisory · Kludex/python-multipart · GitHub

https://github.com/Kludex/python-multipart/security/advisories/GHSA-mj87-hwqh-73pj
github_release Patch Available

Version 0.0.26

Patch available: Kludex/python-multipart 0.0.26

https://github.com/Kludex/python-multipart/releases/tag/0.0.26

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.17-1 ... 0.0.9-1 (14 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.17-1 ... 0.0.9-1 (13 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.20-1, 0.0.20-1.1, 0.0.20-1.1~deb13u1, 0.0.22-1, 0.0.26-1——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.20-1, 0.0.20-1.1, 0.0.20-1.1~deb13u1, 0.0.22-10.0.26-1—
PyPI(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.1 ... 0.0.9 (25 versions)0.0.26—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 39× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 137 total refreshes for this CVE.

  1. 2026-08-25 13:49 UTCEPSS rescore
  2. 2026-08-23 00:19 UTCEPSS rescore
  3. 2026-08-21 23:49 UTCEPSS rescore
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  9. 2026-08-16 06:28 UTCEG score recompute
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  1. 2026-08-06 21:06 UTCEG score recompute
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  23. 2026-07-23 03:11 UTCEG score recompute
  24. 2026-07-22 14:08 UTCEPSS rescore
  25. 2026-07-21 15:24 UTCEPSS rescore
  26. 2026-07-20 17:08 UTCEPSS rescore
  27. 2026-07-20 07:34 UTCOSV refresh
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  74. 2026-06-10 22:18 UTCEPSS rescore
  75. 2026-06-10 13:22 UTCEPSS rescore

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-40347?
CVE-2026-40347 is a medium vulnerability published on April 18, 2026. 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…
When was CVE-2026-40347 disclosed?
CVE-2026-40347 was first published in the National Vulnerability Database on April 18, 2026, with the most recent update on April 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-40347 actively exploited?
CVE-2026-40347 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 72.3% of all scored CVEs.
What is the CVSS score of CVE-2026-40347?
CVE-2026-40347 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-40347?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-40347, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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