CVE-2021-33037

MEDIUMNVD 5.38.4▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.4 because EPSS predicts 75% probability of exploitation within the next 30 days (top 0.5% of all CVEs). NVD baseline CVSS 5.3 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, nvd
Trending — 3 sources updated this weekElevated
5.3
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • 4,784 internet-exposed hosts are running an affected version right now
  • High exploitation likelihood — EPSS 75%
CISA-KEV: Not listedEPSS: 75%CVSS: 5.3Exploit: NoneExposed: 4,784

A fix is available — apply it.

Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer encoding header if the client declared it would only accept an HTTP/1.0 response; - Tomcat honoured the identify encoding; and - Tomcat did not ensure that, if present, the chunked encoding was the final encoding.

Live · internet exposure

4,784 internet-exposed hosts are running an affected version of CVE-2021-33037 right now.

across 115 countries (China, United States, Korea, Republic of, Germany, Brazil)top: tomcat
See the live KEV-Exposure radar →Found passively from public internet-scan data — aggregate, host-redacted.

EchelonGraph is the only CVE feed that fuses live vulnerability intelligence with its own live internet-exposure radar — so you see not just that a CVE is exploited, but how much of the internet is exposed to it right now.

CVSS v3
5.3
EG Score
8.4(high)
EG Risk
72(Track)
EG Risk 72/100SSVC: 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
Severity84% × 45%
Exploitation75% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
99.5%
KEV
Not listed

Published

July 12, 2021

Last Modified

November 21, 2024

References (32)

Vendor Advisories for CVE-2021-33037(1)

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

Patch Availability(3)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntutomcat9-examples (9.0.31-1ubuntu0.2) @ focal2026-05-26ubuntu
redhattomcat2022-07-07redhat
redhatjws5-tomcat-vault-0:1.1.8-4.Final_redhat_00004.1.el8jws2021-11-30redhat

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

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFixed inDependents
org.apache.tomcat:tomcat8.5.0 ... 8.5.9 (54 versions)8.5.68—

Weakness Classification(1)

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

Additional Vendor Advisories

(4)

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 15× in last 7d / 33× 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. 2026-07-23 02:01 UTCEG score recompute▲ 3.10
  2. 2026-07-22 22:48 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
  4. 2026-07-22 14:06 UTCEPSS rescore
  5. 2026-07-21 15:22 UTCEPSS rescore
  6. 2026-07-21 15:22 UTCEPSS rescore
  7. 2026-07-20 17:05 UTCEPSS rescore
  8. 2026-07-19 14:29 UTCEPSS rescore
  9. 2026-07-19 14:29 UTCEPSS rescore
  10. 2026-07-19 02:27 UTCEPSS rescore
  11. 2026-07-18 16:59 UTCOSV refresh
  12. 2026-07-18 10:02 UTCEPSS rescore
  13. 2026-07-18 10:02 UTCEPSS rescore
  14. 2026-07-16 17:00 UTCEPSS rescore
  15. 2026-07-16 17:00 UTCEPSS rescore
  16. 2026-07-15 16:55 UTCEPSS rescore
  17. 2026-07-13 06:10 UTCEPSS rescore
  18. 2026-07-12 05:44 UTCEPSS rescore
  19. 2026-07-12 05:44 UTCEPSS rescore
  20. 2026-07-09 19:07 UTCEPSS rescore
  21. 2026-07-07 13:43 UTCEPSS rescore
  22. 2026-07-04 06:29 UTCEPSS rescore
  23. 2026-07-04 06:29 UTCEPSS rescore
  24. 2026-07-01 15:04 UTCEPSS rescore
  25. 2026-06-30 23:48 UTCOSV refresh
Show 55 more
  1. 2026-06-28 14:05 UTCEPSS rescore
  2. 2026-06-28 04:54 UTCEPSS rescore
  3. 2026-06-28 04:54 UTCEPSS rescore
  4. 2026-06-27 03:06 UTCEPSS rescore
  5. 2026-06-25 13:48 UTCEPSS rescore
  6. 2026-06-25 13:48 UTCEPSS rescore
  7. 2026-06-23 21:31 UTCEPSS rescore
  8. 2026-06-23 21:31 UTCEPSS rescore
  9. 2026-06-21 01:58 UTCEPSS rescore
  10. 2026-06-21 01:58 UTCEPSS rescore
  11. 2026-06-17 17:51 UTCEPSS rescore
  12. 2026-06-15 17:46 UTCEPSS rescore
  13. 2026-06-14 23:15 UTCEPSS rescore
  14. 2026-06-13 22:58 UTCEPSS rescore
  15. 2026-06-13 22:58 UTCEPSS rescore
  16. 2026-06-13 02:06 UTCOSV refresh
  17. 2026-06-12 23:10 UTCEPSS rescore
  18. 2026-06-12 23:10 UTCEPSS rescore
  19. 2026-06-11 13:58 UTCEPSS rescore
  20. 2026-06-10 22:16 UTCEPSS rescore
  21. 2026-06-10 13:20 UTCEPSS rescore
  22. 2026-06-08 14:15 UTCEPSS rescore
  23. 2026-06-08 14:15 UTCEPSS rescore
  24. 2026-06-07 15:23 UTCEPSS rescore
  25. 2026-06-07 15:23 UTCEPSS rescore
  26. 2026-06-06 13:46 UTCEPSS rescore
  27. 2026-06-06 13:46 UTCEPSS rescore
  28. 2026-06-06 13:46 UTCEPSS rescore
  29. 2026-06-05 22:45 UTCEPSS rescore
  30. 2026-06-05 06:09 UTCEPSS rescore
  31. 2026-06-05 06:09 UTCEPSS rescore
  32. 2026-06-04 13:10 UTCEPSS rescore
  33. 2026-06-04 13:10 UTCEPSS rescore
  34. 2026-06-02 20:11 UTCEPSS rescore
  35. 2026-06-02 20:11 UTCEPSS rescore
  36. 2026-06-01 13:50 UTCEPSS rescore
  37. 2026-06-01 13:50 UTCEPSS rescore
  38. 2026-05-31 22:29 UTCEPSS rescore
  39. 2026-05-31 22:29 UTCEPSS rescore
  40. 2026-05-31 00:15 UTCEPSS rescore
  41. 2026-05-31 00:15 UTCEPSS rescore
  42. 2026-05-29 13:42 UTCEPSS rescore
  43. 2026-05-29 13:42 UTCEPSS rescore
  44. 2026-05-28 13:43 UTCEPSS rescore
  45. 2026-05-28 13:43 UTCEPSS rescore
  46. 2026-05-27 13:39 UTCEPSS rescore
  47. 2026-05-27 13:39 UTCEPSS rescore
  48. 2026-05-27 13:39 UTCEPSS rescore
  49. 2026-05-26 13:56 UTCVendor advisory
  50. 2026-05-26 13:56 UTCEG score recompute
  51. 2026-05-26 13:56 UTCVendor advisory
  52. 2026-05-26 13:42 UTCEPSS rescore
  53. 2026-05-26 07:17 UTCEPSS rescore
  54. 2026-05-26 07:17 UTCEPSS rescore
  55. 2026-05-26 07:17 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-33037?
CVE-2021-33037 is a medium vulnerability published on July 12, 2021. Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer…
When was CVE-2021-33037 disclosed?
CVE-2021-33037 was first published in the National Vulnerability Database on July 12, 2021, 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-2021-33037 actively exploited?
CVE-2021-33037 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-33037?
CVE-2021-33037 has a CVSS v3 base score of 5.3 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.4.
How do I remediate CVE-2021-33037?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-33037, 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-2021-33037

Explore →

Is Your Infrastructure Affected by CVE-2021-33037?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs