CVE-2021-33620

HIGHNVD 6.58.8▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.8 because EPSS predicts 80% probability of exploitation within the next 30 days (top 0.4% of all CVEs). NVD baseline CVSS 6.5 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, ghsa, nvd
Elevated
8.8EG
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 80%
CISA-KEV: Not listedEPSS PROB: 80%CVSS: 6.5Exploit: Elevated riskExposed: 0

A fix is available — apply it.

Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause a denial of service (affecting availability to all clients) via an HTTP response. The issue trigger is a header that can be expected to exist in HTTP traffic without any malicious intent by the server.

CVSS v3
6.5
EG Score
8.8(high)
EG Risk
76(Track)
EG Risk 76/100SSVC: 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
Severity88% × 45%
Exploitation80% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
80%
EPSS %ILE
100%
KEV
Not listed

Published

May 28, 2021

Last Modified

November 21, 2024

References (16)

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatsquid:4-8050020210618131503.b4937e532021-11-09redhat

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

(16 across 16 ecosystems)
Alpine:v3.15(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.16(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.17(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.18(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.19(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.20(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.21(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.22(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.23(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Alpine:v3.24(1)
PackageVulnerable rangeFixed inDependents
squid—5.0.6-r0—
Debian:10(1)
PackageVulnerable rangeFixed inDependents
squid4.6-1 ... 4.6-1+deb10u5 (6 versions)4.6-1+deb10u6—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
squid—4.13-10—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
squid—4.13-10—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
squid—4.13-10—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
squid—4.13-10—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
squid33.5.23-5 ... 3.5.23-5+deb9u6 (7 versions)3.5.23-5+deb9u7—

Weakness Classification(1)

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

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 3× in last 7d / 17× 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. 2026-09-18 19:23 UTCEPSS rescore
  2. 2026-09-16 14:05 UTCEPSS rescore
  3. 2026-09-16 14:05 UTCEPSS rescore
  4. 2026-09-13 16:43 UTCEPSS rescore
  5. 2026-09-12 14:57 UTCEPSS rescore
  6. 2026-09-11 14:49 UTCEPSS rescore
  7. 2026-09-06 16:01 UTCOSV refresh
  8. 2026-09-06 13:45 UTCEPSS rescore
  9. 2026-09-06 13:45 UTCEPSS rescore
  10. 2026-09-05 15:25 UTCEPSS rescore
  11. 2026-09-04 05:03 UTCEPSS rescore
  12. 2026-09-01 13:50 UTCEPSS rescore
  13. 2026-08-30 19:14 UTCEPSS rescore
  14. 2026-08-28 21:37 UTCEPSS rescore
  15. 2026-08-26 14:42 UTCEPSS rescore
  16. 2026-08-25 13:46 UTCEPSS rescore
  17. 2026-08-24 14:13 UTCEPSS rescore
  18. 2026-08-20 22:52 UTCEPSS rescore
  19. 2026-08-20 02:04 UTCOSV refresh
  20. 2026-08-19 17:01 UTCEPSS rescore
  21. 2026-08-16 02:11 UTCEPSS rescore
  22. 2026-08-16 02:11 UTCEPSS rescore
  23. 2026-08-13 21:57 UTCEPSS rescore
  24. 2026-08-12 13:48 UTCEPSS rescore
  25. 2026-08-06 13:43 UTCEPSS rescore
Show 71 more
  1. 2026-08-05 19:14 UTCEPSS rescore
  2. 2026-08-04 21:18 UTCOSV refresh
  3. 2026-08-04 15:06 UTCEPSS rescore
  4. 2026-07-30 16:25 UTCEPSS rescore
  5. 2026-07-30 01:28 UTCEPSS rescore
  6. 2026-07-26 14:52 UTCEPSS rescore
  7. 2026-07-26 14:52 UTCEPSS rescore
  8. 2026-07-25 14:15 UTCEPSS rescore
  9. 2026-07-24 14:15 UTCEPSS rescore
  10. 2026-07-23 14:16 UTCEPSS rescore
  11. 2026-07-23 14:16 UTCEPSS rescore
  12. 2026-07-23 02:01 UTCEG score recompute▲ 2.30
  13. 2026-07-22 22:48 UTCEG score recompute
  14. 2026-07-22 14:06 UTCEPSS rescore
  15. 2026-07-22 14:06 UTCEPSS rescore
  16. 2026-07-20 17:05 UTCEPSS rescore
  17. 2026-07-18 19:29 UTCOSV refresh
  18. 2026-07-16 17:00 UTCEPSS rescore
  19. 2026-07-16 17:00 UTCEPSS rescore
  20. 2026-07-15 16:55 UTCEPSS rescore
  21. 2026-07-13 06:10 UTCEPSS rescore
  22. 2026-07-09 19:07 UTCEPSS rescore
  23. 2026-07-06 02:21 UTCEPSS rescore
  24. 2026-07-01 02:18 UTCOSV refresh
  25. 2026-06-29 14:04 UTCEPSS rescore
  26. 2026-06-25 13:48 UTCEPSS rescore
  27. 2026-06-25 13:48 UTCEPSS rescore
  28. 2026-06-23 21:31 UTCEPSS rescore
  29. 2026-06-23 21:31 UTCEPSS rescore
  30. 2026-06-21 14:55 UTCEPSS rescore
  31. 2026-06-17 17:51 UTCEPSS rescore
  32. 2026-06-16 17:51 UTCEPSS rescore
  33. 2026-06-16 17:51 UTCEPSS rescore
  34. 2026-06-15 17:46 UTCEPSS rescore
  35. 2026-06-13 22:58 UTCEPSS rescore
  36. 2026-06-13 22:58 UTCEPSS rescore
  37. 2026-06-13 04:43 UTCOSV refresh
  38. 2026-06-12 23:10 UTCEPSS rescore
  39. 2026-06-12 23:10 UTCEPSS rescore
  40. 2026-06-11 13:58 UTCEPSS rescore
  41. 2026-06-10 22:16 UTCEPSS rescore
  42. 2026-06-10 13:20 UTCEPSS rescore
  43. 2026-06-08 14:15 UTCEPSS rescore
  44. 2026-06-08 14:15 UTCEPSS rescore
  45. 2026-06-07 15:23 UTCEPSS rescore
  46. 2026-06-07 15:23 UTCEPSS rescore
  47. 2026-06-06 13:46 UTCEPSS rescore
  48. 2026-06-06 13:46 UTCEPSS rescore
  49. 2026-06-06 13:46 UTCEPSS rescore
  50. 2026-06-05 22:45 UTCEPSS rescore
  51. 2026-06-05 06:09 UTCEPSS rescore
  52. 2026-06-05 06:09 UTCEPSS rescore
  53. 2026-06-04 13:10 UTCEPSS rescore
  54. 2026-06-04 13:10 UTCEPSS rescore
  55. 2026-06-02 20:11 UTCEPSS rescore
  56. 2026-06-02 20:11 UTCEPSS rescore
  57. 2026-05-31 22:29 UTCEPSS rescore
  58. 2026-05-31 22:29 UTCEPSS rescore
  59. 2026-05-31 00:15 UTCEPSS rescore
  60. 2026-05-31 00:15 UTCEPSS rescore
  61. 2026-05-29 13:42 UTCEPSS rescore
  62. 2026-05-29 13:42 UTCEPSS rescore
  63. 2026-05-28 13:43 UTCEPSS rescore
  64. 2026-05-28 13:43 UTCEPSS rescore
  65. 2026-05-27 13:39 UTCEPSS rescore
  66. 2026-05-27 13:39 UTCEPSS rescore
  67. 2026-05-27 13:39 UTCEPSS rescore
  68. 2026-05-26 15:56 UTCEG score recompute
  69. 2026-05-26 15:56 UTCVendor advisory
  70. 2026-05-26 15:55 UTCGHSA enrichment
  71. 2026-05-26 13:42 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-33620?
CVE-2021-33620 is a high vulnerability published on May 28, 2021. Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause a denial of service (affecting availability to all clients) via an HTTP response. The issue trigger is a header that can be expected to exist in HTTP traffic without any malicious intent by the server.
When was CVE-2021-33620 disclosed?
CVE-2021-33620 was first published in the National Vulnerability Database on May 28, 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-2021-33620 actively exploited?
CVE-2021-33620 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 80% probability of exploitation in the next 30 days, which ranks it in the top 0.4% of all scored CVEs.
What is the CVSS score of CVE-2021-33620?
CVE-2021-33620 has a CVSS v3 base score of 6.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.8.
How do I remediate CVE-2021-33620?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-33620, 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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