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.
CVE-2026-40347
MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 5.3 under NVD CVSS v3. EPSS exploit probability: 0.0%, top 94% 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
5.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 5.3Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.3
- EG Score
- 5.3(medium)
- EPSS
- 27.2%
- KEV
- Not listed
Published
April 18, 2026
Last Modified
April 24, 2026
References (2)
- security-advisories@githubhttps://github.com/Kludex/python-multipart/releases/tag/0.0.26
- security-advisories@githubhttps://github.com/Kludex/python-multipart/security/advisories/GHSA-mj87-hwqh-73pj
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 27.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
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.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-40347
Is Your Infrastructure Affected by CVE-2026-40347?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.