CVE-2020-5236

MEDIUMNVD 5.75.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.7 under NVD CVSS v3. EPSS exploit probability: 2.4% (83rd percentile of EPSS-scored CVEs). 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
5.7EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 2.4%CVSS: 5.7Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

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
5.7MEDIUMmedium confidence
EG Risk
46
EG Risk 46/100CISA SSVC

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
Severity57% × 45%
Exploitation40% × 40%
Automatability30% × 15%
CISA SSVC: Track at low or medium mission impact; Track* or Attend at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
2.4%
EPSS %ILE
83rd
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* or Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (EG-KEV: elevated) · Automatable unknown (not published for this CVE) · Technical impact partial (CVSS below 9.0). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

February 4, 2020

Last Modified

November 21, 2024

References (4)

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFix by version rangeDependents
waitress0.1 ... 1.4.2 (40 versions)
  • 1.4.2 up to 1.4.3: fixed in 1.4.3
  • every version up to 1.4.3: fixed in 1.4.3
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 6× in last 7d / 27× 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 172 total refreshes for this CVE.

  1. 2026-10-09 20:04 UTCEPSS rescore
  2. 2026-10-08 16:39 UTCEPSS rescore
  3. 2026-10-07 23:44 UTCEPSS rescore
  4. 2026-10-06 15:13 UTCEPSS rescore
  5. 2026-10-05 17:40 UTCEPSS rescore
  6. 2026-10-04 23:18 UTCEPSS rescore
  7. 2026-10-03 14:22 UTCEPSS rescore
  8. 2026-10-03 14:22 UTCEPSS rescore
  9. 2026-10-02 16:22 UTCEPSS rescore
  10. 2026-10-01 19:46 UTCEPSS rescore
  11. 2026-09-30 15:20 UTCEG score recompute
  12. 2026-09-30 14:59 UTCEPSS rescore
  13. 2026-09-27 13:41 UTCEPSS rescore
  14. 2026-09-27 10:07 UTCOSV refresh
  15. 2026-09-26 15:54 UTCEPSS rescore
  16. 2026-09-26 15:54 UTCEPSS rescore
  17. 2026-09-26 00:21 UTCEPSS rescore
  18. 2026-09-24 14:00 UTCEPSS rescore
  19. 2026-09-22 14:44 UTCEPSS rescore
  20. 2026-09-21 20:28 UTCEPSS rescore
  21. 2026-09-19 15:37 UTCEPSS rescore
  22. 2026-09-18 19:23 UTCEPSS rescore
  23. 2026-09-17 19:22 UTCEPSS rescore
  24. 2026-09-16 14:04 UTCEPSS rescore
  25. 2026-09-15 03:06 UTCEPSS rescore
Show 75 more
  1. 2026-09-13 16:43 UTCEPSS rescore
  2. 2026-09-12 14:57 UTCEPSS rescore
  3. 2026-09-08 21:56 UTCEPSS rescore
  4. 2026-09-07 19:51 UTCOSV refresh
  5. 2026-09-07 15:58 UTCEPSS rescore
  6. 2026-09-06 13:44 UTCEPSS rescore
  7. 2026-09-05 15:25 UTCEPSS rescore
  8. 2026-09-04 13:57 UTCEPSS rescore
  9. 2026-09-04 13:57 UTCEPSS rescore
  10. 2026-09-04 05:03 UTCEPSS rescore
  11. 2026-09-02 14:08 UTCEPSS rescore
  12. 2026-09-01 03:32 UTCEPSS rescore
  13. 2026-08-30 19:14 UTCEPSS rescore
  14. 2026-08-30 01:19 UTCEPSS rescore
  15. 2026-08-28 21:37 UTCEPSS rescore
  16. 2026-08-27 14:21 UTCEPSS rescore
  17. 2026-08-26 14:42 UTCEPSS rescore
  18. 2026-08-21 23:45 UTCEPSS rescore
  19. 2026-08-21 05:14 UTCOSV refresh
  20. 2026-08-19 17:00 UTCEPSS rescore
  21. 2026-08-18 13:44 UTCEPSS rescore
  22. 2026-08-17 13:43 UTCEPSS rescore
  23. 2026-08-17 13:43 UTCEPSS rescore
  24. 2026-08-16 14:52 UTCEPSS rescore
  25. 2026-08-16 02:11 UTCEPSS rescore
  26. 2026-08-15 01:27 UTCEPSS rescore
  27. 2026-08-13 21:57 UTCEPSS rescore
  28. 2026-08-12 13:47 UTCEPSS rescore
  29. 2026-08-09 13:43 UTCEPSS rescore
  30. 2026-08-08 16:33 UTCEPSS rescore
  31. 2026-08-07 16:23 UTCEPSS rescore
  32. 2026-08-06 13:43 UTCEPSS rescore
  33. 2026-08-05 20:24 UTCOSV refresh
  34. 2026-08-05 19:14 UTCEPSS rescore
  35. 2026-08-04 15:06 UTCEPSS rescore
  36. 2026-08-04 10:34 UTCEPSS rescore
  37. 2026-08-02 02:24 UTCEPSS rescore
  38. 2026-08-01 04:12 UTCEPSS rescore
  39. 2026-07-30 16:25 UTCEPSS rescore
  40. 2026-07-30 01:27 UTCEPSS rescore
  41. 2026-07-28 15:33 UTCEPSS rescore
  42. 2026-07-26 14:52 UTCEPSS rescore
  43. 2026-07-25 14:15 UTCEPSS rescore
  44. 2026-07-24 14:15 UTCEPSS rescore
  45. 2026-07-23 14:15 UTCEPSS rescore
  46. 2026-07-23 01:54 UTCEG score recompute
  47. 2026-07-22 22:40 UTCEG score recompute
  48. 2026-07-22 14:05 UTCEPSS rescore
  49. 2026-07-21 15:22 UTCEPSS rescore
  50. 2026-07-21 15:22 UTCEPSS rescore
  51. 2026-07-20 17:04 UTCEPSS rescore
  52. 2026-07-20 17:04 UTCEPSS rescore
  53. 2026-07-19 20:18 UTCOSV refresh
  54. 2026-07-19 14:28 UTCEPSS rescore
  55. 2026-07-19 14:28 UTCEPSS rescore
  56. 2026-07-19 02:26 UTCEPSS rescore
  57. 2026-07-19 02:26 UTCEPSS rescore
  58. 2026-07-18 10:02 UTCEPSS rescore
  59. 2026-07-16 17:00 UTCEPSS rescore
  60. 2026-07-15 16:55 UTCEPSS rescore
  61. 2026-07-15 16:55 UTCEPSS rescore
  62. 2026-07-15 01:57 UTCEPSS rescore
  63. 2026-07-13 22:27 UTCEPSS rescore
  64. 2026-07-13 22:27 UTCEPSS rescore
  65. 2026-07-13 06:10 UTCEPSS rescore
  66. 2026-07-13 06:10 UTCEPSS rescore
  67. 2026-07-12 05:44 UTCEPSS rescore
  68. 2026-07-12 05:44 UTCEPSS rescore
  69. 2026-07-11 08:25 UTCEPSS rescore
  70. 2026-07-11 08:25 UTCEPSS rescore
  71. 2026-07-09 19:07 UTCEPSS rescore
  72. 2026-07-08 15:12 UTCEPSS rescore
  73. 2026-07-07 13:43 UTCEPSS rescore
  74. 2026-07-06 16:25 UTCEPSS rescore
  75. 2026-07-06 02:21 UTCEPSS rescore

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 product + 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 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 2.4% probability of exploitation in the next 30 days (83rd percentile of EPSS-scored CVEs).
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?
A fix for CVE-2020-5236 is available: update to the fixed version the vendor names in its advisory.

Dependency Blast Radius

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