CVE-2021-3733

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

Score 6.5 from GitHub Security Advisory published 2022-03-11. NVD baseline CVSS 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 5%CVSS: 6.5Exploit: None knownExposed: 0

A fix is available — apply it.

There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is sent by the server to the client. The greatest threat that this flaw poses is to application availability.

CVSS v3
6.5
EG Score
6.5(medium)
EG Risk
36(Track)
EG Risk 36/100SSVC: 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
Severity65% × 45%
Exploitation5% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
5%
EPSS %ILE
91%
KEV
Not listed

Published

March 10, 2022

Last Modified

November 3, 2025

References (17)

Vendor Advisories for CVE-2021-3733(6)

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

Patch Availability(10)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntupython3.4-venv (3.4.3-1ubuntu1~14.04.7+esm11) @ trusty2026-05-26ubuntu
ubuntulibpython3.6-minimal (3.6.9-1~18.04ubuntu1.6) @ bionic2026-05-26ubuntu
ubuntulibpython3.7 (3.7.5-2ubuntu1~18.04.2) @ bionic2026-05-26ubuntu
ubuntupython3.8-venv (3.8.0-3ubuntu1~18.04.2+esm2) @ bionic2026-05-26ubuntu
redhatpython38-devel:3.8-8060020220120164031.5294be162022-05-10redhat
redhatpython27:2.7-8060020220210185952.8cdc22682022-05-10redhat
redhatpython27-python-0:2.7.18-4.el72022-05-02redhat
redhatpython39-devel:3.9-8050020210811100211.d428a79b2021-11-09redhat
redhatpython3-0:3.6.8-39.el8_42021-11-02redhat
redhatrh-python38-python-urllib3-0:1.25.7-7.el72021-08-24redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(9 across 6 ecosystems)
Debian:11(3)
PackageVulnerable rangeFixed inDependents
pypy3—7.3.5+dfsg-2—
python2.72.7.18-10 ... 2.7.18-9 (10 versions)——
python3.93.9.2-1, 3.9.2-1+deb11u13.9.2-1+deb11u2—
Debian:10(2)
PackageVulnerable rangeFixed inDependents
python2.72.7.16-2, 2.7.16-2+deb10u12.7.16-2+deb10u2—
python3.73.7.3-2, 3.7.3-2+deb10u1, 3.7.3-2+deb10u2, 3.7.3-2+deb10u3, 3.7.3-2+deb10u43.7.3-2+deb10u5—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
pypy3—7.3.5+dfsg-2—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
pypy3—7.3.5+dfsg-2—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
pypy3—7.3.5+dfsg-2—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
python3.53.5.3-1, 3.5.3-1+deb9u1, 3.5.3-1+deb9u2, 3.5.3-1+deb9u3, 3.5.3-1+deb9u43.5.3-1+deb9u5—

Weakness Classification(1)

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

Additional Vendor Advisories

(5)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 8× in last 7d / 32× 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 156 total refreshes for this CVE.

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

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-3733?
CVE-2021-3733 is a medium vulnerability published on March 10, 2022. There's a flaw in urllib's AbstractBasicAuthHandler class. An attacker who controls a malicious HTTP server that an HTTP client (such as web browser) connects to, could trigger a Regular Expression Denial of Service (ReDOS) during an authentication request with a specially crafted payload that is…
When was CVE-2021-3733 disclosed?
CVE-2021-3733 was first published in the National Vulnerability Database on March 10, 2022, with the most recent update on November 3, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-3733 actively exploited?
CVE-2021-3733 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 5% probability of exploitation in the next 30 days, which ranks it in the top 8.8% of all scored CVEs.
What is the CVSS score of CVE-2021-3733?
CVE-2021-3733 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2021-3733?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-3733, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-3733

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