CVE-2020-5236

MEDIUMNVD 5.75.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.7 under NVD CVSS v3. EPSS exploit probability: 13.3%, top 6% 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
Elevated
5.7
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 3%CVSS: 5.7Exploit: NoneExposed: 0

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

Waitress version 1.4.2 allows a DOS attack When waitress receives a header that contains invalid characters. When a header like "Bad-header: xxxxxxxxxxxxxxx\x10" is received, it will cause the regular expression engine to catastrophically backtrack causing the process to use 100% CPU time and blocking any other interactions. This allows an attacker to send a single request with an invalid header and take the service offline. This issue was introduced in version 1.4.2 when the regular expression was updated to attempt to match the behaviour required by errata associated with RFC7230. The regular expression that is used to validate incoming headers has been updated in version 1.4.3, it is recommended that people upgrade to the new version of Waitress as soon as possible.

CVSS v3
5.7
EG Score
5.7(medium)
EPSS
83.7%
KEV
Not listed

Published

February 4, 2020

Last Modified

November 21, 2024

References (4)

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
waitress0.1 ... 1.4.2 (40 versions)1.4.3—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 48× 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. 2026-07-12 05:44 UTCEPSS rescore
  2. 2026-07-12 05:44 UTCEPSS rescore
  3. 2026-07-11 08:25 UTCEPSS rescore
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  5. 2026-07-09 19:07 UTCEPSS rescore
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  7. 2026-07-07 13:43 UTCEPSS rescore
  8. 2026-07-06 16:25 UTCEPSS rescore
  9. 2026-07-06 02:21 UTCEPSS rescore
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  11. 2026-07-05 02:28 UTCEPSS rescore
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  13. 2026-07-04 06:29 UTCEPSS rescore
  14. 2026-07-04 06:29 UTCEPSS rescore
  15. 2026-07-02 16:57 UTCEPSS rescore
  16. 2026-07-02 11:11 UTCOSV refresh
  17. 2026-07-01 15:03 UTCEPSS rescore
  18. 2026-06-30 23:20 UTCEPSS rescore
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  20. 2026-06-28 14:05 UTCEPSS rescore
  21. 2026-06-28 04:54 UTCEPSS rescore
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  25. 2026-06-25 13:48 UTCEPSS rescore
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  1. 2026-06-25 13:48 UTCEPSS rescore
  2. 2026-06-24 14:03 UTCEPSS rescore
  3. 2026-06-24 14:03 UTCEPSS rescore
  4. 2026-06-23 21:31 UTCEPSS rescore
  5. 2026-06-23 21:31 UTCEPSS rescore
  6. 2026-06-22 14:23 UTCEPSS rescore
  7. 2026-06-21 14:54 UTCEPSS rescore
  8. 2026-06-21 14:54 UTCEPSS rescore
  9. 2026-06-21 01:57 UTCEPSS rescore
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  11. 2026-06-19 19:24 UTCEPSS rescore
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  13. 2026-06-18 17:51 UTCEPSS rescore
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  17. 2026-06-15 17:46 UTCEPSS rescore
  18. 2026-06-14 23:15 UTCEPSS rescore
  19. 2026-06-14 09:43 UTCOSV refresh
  20. 2026-06-13 22:58 UTCEPSS rescore
  21. 2026-06-13 22:58 UTCEPSS rescore
  22. 2026-06-12 23:10 UTCEPSS rescore
  23. 2026-06-12 23:10 UTCEPSS rescore
  24. 2026-06-11 13:58 UTCEPSS rescore
  25. 2026-06-11 13:58 UTCEPSS rescore
  26. 2026-06-10 22:16 UTCEPSS rescore
  27. 2026-06-10 13:20 UTCEPSS rescore
  28. 2026-06-07 15:23 UTCEPSS rescore
  29. 2026-06-07 15:23 UTCEPSS rescore
  30. 2026-06-06 13:46 UTCEPSS rescore
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  35. 2026-06-05 06:08 UTCEPSS rescore
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  37. 2026-06-04 13:10 UTCEPSS rescore
  38. 2026-06-04 13:10 UTCEPSS rescore
  39. 2026-06-02 20:11 UTCEPSS rescore
  40. 2026-06-02 20:11 UTCEPSS rescore
  41. 2026-06-01 13:50 UTCEPSS rescore
  42. 2026-05-31 22:29 UTCEPSS rescore
  43. 2026-05-31 22:29 UTCEPSS rescore
  44. 2026-05-31 00:15 UTCEPSS rescore
  45. 2026-05-31 00:15 UTCEPSS rescore
  46. 2026-05-29 13:42 UTCEPSS rescore
  47. 2026-05-28 13:43 UTCEPSS rescore
  48. 2026-05-28 13:43 UTCEPSS rescore
  49. 2026-05-27 13:39 UTCEPSS rescore
  50. 2026-05-27 13:39 UTCEPSS rescore
  51. 2026-05-27 08:20 UTCEG score recompute
  52. 2026-05-26 13:42 UTCEPSS rescore
  53. 2026-05-26 13:42 UTCEPSS rescore
  54. 2026-05-26 07:17 UTCEPSS rescore
  55. 2026-05-26 07:17 UTCEPSS rescore
  56. 2026-05-25 21:46 UTCOSV refresh

Publicly available exploits

(1 reference)

Working exploit code is in the public domain (1 GitHub PoC). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCmotikan2010/CVE-2020-5236
    First seen Feb 6, 2020

    Waitress 1.4.2 ReDoS - CVE-2020-5236 (Blog Sample Code)

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2020-5236?
CVE-2020-5236 is a medium vulnerability published on February 4, 2020. Waitress version 1.4.2 allows a DOS attack When waitress receives a header that contains invalid characters. When a header like "Bad-header: xxxxxxxxxxxxxxx\x10" is received, it will cause the regular expression engine to catastrophically backtrack causing the process to use 100% CPU time and…
When was CVE-2020-5236 disclosed?
CVE-2020-5236 was first published in the National Vulnerability Database on February 4, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-5236 actively exploited?
CVE-2020-5236 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 83.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2020-5236?
CVE-2020-5236 has a CVSS v3 base score of 5.7 (NVD).
How do I remediate CVE-2020-5236?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-5236, 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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