CVE-2026-53539

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 82% 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, secondary
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 7.5Exploit: NoneExposed: 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. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.

CVSS v3
7.5
EG Score
7.5(medium)
EPSS
17.7%
KEV
Not listed

Published

June 15, 2026

Last Modified

June 26, 2026

Advisory Details (1)

Auto-updated Jun 22, 2026
Patch available. Sources: github.
github Patch Available

Quadratic-time querystring parsing with semicolon separators causes CPU denial of service · Advisory · Kludex/python-multipart · GitHub

https://github.com/Kludex/python-multipart/security/advisories/GHSA-5rvq-cxj2-64vf

Vendor Advisories for CVE-2026-53539(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
python-multipart0.0.1 ... 0.0.9 (29 versions)0.0.30—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 22× in last 7d / 59× 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.

  1. 2026-07-07 00:16 UTCEG score recompute
  2. 2026-07-06 16:27 UTCEPSS rescore
  3. 2026-07-06 16:27 UTCEPSS rescore
  4. 2026-07-06 02:23 UTCEPSS rescore
  5. 2026-07-06 02:23 UTCEPSS rescore
  6. 2026-07-06 00:16 UTCEG score recompute
  7. 2026-07-05 11:31 UTCEG score recompute
  8. 2026-07-05 02:31 UTCEPSS rescore
  9. 2026-07-05 02:30 UTCEPSS rescore
  10. 2026-07-04 22:44 UTCEG score recompute
  11. 2026-07-04 09:58 UTCEG score recompute
  12. 2026-07-04 06:31 UTCEPSS rescore
  13. 2026-07-04 06:31 UTCEPSS rescore
  14. 2026-07-03 14:12 UTCEG score recompute
  15. 2026-07-03 00:39 UTCEG score recompute
  16. 2026-07-02 11:48 UTCEG score recompute
  17. 2026-07-01 22:43 UTCEG score recompute
  18. 2026-07-01 15:07 UTCEPSS rescore
  19. 2026-07-01 09:13 UTCEG score recompute
  20. 2026-06-30 23:22 UTCEPSS rescore
  21. 2026-06-30 20:28 UTCEG score recompute
  22. 2026-06-30 07:39 UTCEG score recompute
  23. 2026-06-29 18:52 UTCEG score recompute
  24. 2026-06-29 14:06 UTCEPSS rescore
  25. 2026-06-29 14:06 UTCEPSS rescore
Show 34 more
  1. 2026-06-29 06:07 UTCEG score recompute
  2. 2026-06-28 17:18 UTCEG score recompute
  3. 2026-06-28 14:07 UTCEPSS rescore
  4. 2026-06-28 04:56 UTCEPSS rescore
  5. 2026-06-28 04:56 UTCEPSS rescore
  6. 2026-06-28 04:34 UTCEG score recompute
  7. 2026-06-27 15:47 UTCEG score recompute
  8. 2026-06-27 03:08 UTCEPSS rescore
  9. 2026-06-27 03:02 UTCEG score recompute
  10. 2026-06-26 14:16 UTCEG score recompute
  11. 2026-06-26 01:19 UTCEG score recompute
  12. 2026-06-25 13:49 UTCEPSS rescore
  13. 2026-06-25 12:35 UTCEG score recompute
  14. 2026-06-24 23:50 UTCEG score recompute
  15. 2026-06-24 14:05 UTCEPSS rescore
  16. 2026-06-24 11:06 UTCEG score recompute
  17. 2026-06-23 22:17 UTCEG score recompute
  18. 2026-06-23 21:33 UTCEPSS rescore
  19. 2026-06-23 21:33 UTCEPSS rescore
  20. 2026-06-23 08:55 UTCEG score recompute
  21. 2026-06-22 20:10 UTCEG score recompute
  22. 2026-06-22 07:10 UTCEG score recompute
  23. 2026-06-21 18:22 UTCEG score recompute
  24. 2026-06-21 04:42 UTCEG score recompute
  25. 2026-06-20 15:42 UTCEG score recompute
  26. 2026-06-20 02:54 UTCEG score recompute
  27. 2026-06-19 14:09 UTCEG score recompute
  28. 2026-06-19 01:23 UTCEG score recompute
  29. 2026-06-18 12:35 UTCEG score recompute
  30. 2026-06-17 23:46 UTCEG score recompute
  31. 2026-06-17 11:02 UTCEG score recompute
  32. 2026-06-16 22:15 UTCEG score recompute
  33. 2026-06-16 09:30 UTCEG score recompute
  34. 2026-06-15 20:46 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-53539?
CVE-2026-53539 is a high vulnerability published on June 15, 2026. Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead…
When was CVE-2026-53539 disclosed?
CVE-2026-53539 was first published in the National Vulnerability Database on June 15, 2026, with the most recent update on June 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-53539 actively exploited?
CVE-2026-53539 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 17.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-53539?
CVE-2026-53539 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-53539?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-53539, 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

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