CVE-2021-28662

MEDIUMNVD 6.58.4▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.4 because EPSS predicts 72% probability of exploitation within the next 30 days (top 0.6% of all CVEs). NVD baseline CVSS 6.5 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, nvd
Elevated
6.5
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 72%
CISA-KEV: Not listedEPSS: 72%CVSS: 6.5Exploit: NoneExposed: 0

A fix is available — apply it.

An issue was discovered in Squid 4.x before 4.15 and 5.x before 5.0.6. If a remote server sends a certain response header over HTTP or HTTPS, there is a denial of service. This header can plausibly occur in benign network traffic.

CVSS v3
6.5
EG Score
8.4(high)
EG Risk
71(Track)
EG Risk 71/100SSVC: 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%
Exploitation72% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
99.4%
KEV
Not listed

Published

May 27, 2021

Last Modified

November 21, 2024

References (16)

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntusquid3 (3.5.27-1ubuntu1.11) @ bionic2026-05-23ubuntu
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.

Weakness Classification(1)

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

All Vendor Advisories

(2)

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 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.

  1. 2026-07-23 01:59 UTCEG score recompute▲ 1.90
  2. 2026-07-22 22:46 UTCEG score recompute
  3. 2026-07-22 14:06 UTCEPSS rescore
  4. 2026-07-22 14:06 UTCEPSS rescore
  5. 2026-07-20 17:05 UTCEPSS rescore
  6. 2026-07-16 17:00 UTCEPSS rescore
  7. 2026-07-15 16:55 UTCEPSS rescore
  8. 2026-07-15 16:55 UTCEPSS rescore
  9. 2026-07-15 01:58 UTCEPSS rescore
  10. 2026-07-13 06:10 UTCEPSS rescore
  11. 2026-07-13 03:38 UTCOSV refresh
  12. 2026-07-12 05:44 UTCEPSS rescore
  13. 2026-07-12 05:44 UTCEPSS rescore
  14. 2026-07-09 19:07 UTCEPSS rescore
  15. 2026-07-05 02:28 UTCEPSS rescore
  16. 2026-07-02 16:57 UTCEPSS rescore
  17. 2026-07-01 15:03 UTCEPSS rescore
  18. 2026-06-28 14:05 UTCEPSS rescore
  19. 2026-06-28 04:54 UTCEPSS rescore
  20. 2026-06-28 04:54 UTCEPSS rescore
  21. 2026-06-25 13:48 UTCEPSS rescore
  22. 2026-06-25 13:48 UTCEPSS rescore
  23. 2026-06-24 14:03 UTCEPSS rescore
  24. 2026-06-24 14:03 UTCEPSS rescore
  25. 2026-06-24 13:32 UTCOSV refresh
Show 46 more
  1. 2026-06-23 21:31 UTCEPSS rescore
  2. 2026-06-23 21:31 UTCEPSS rescore
  3. 2026-06-21 14:55 UTCEPSS rescore
  4. 2026-06-21 14:54 UTCEPSS rescore
  5. 2026-06-21 01:58 UTCEPSS rescore
  6. 2026-06-21 01:58 UTCEPSS rescore
  7. 2026-06-18 17:51 UTCEPSS rescore
  8. 2026-06-18 17:51 UTCEPSS rescore
  9. 2026-06-17 17:51 UTCEPSS rescore
  10. 2026-06-16 17:51 UTCEPSS rescore
  11. 2026-06-15 17:46 UTCEPSS rescore
  12. 2026-06-14 23:15 UTCEPSS rescore
  13. 2026-06-13 22:58 UTCEPSS rescore
  14. 2026-06-13 22:58 UTCEPSS rescore
  15. 2026-06-12 23:10 UTCEPSS rescore
  16. 2026-06-11 13:58 UTCEPSS rescore
  17. 2026-06-10 22:16 UTCEPSS rescore
  18. 2026-06-10 13:20 UTCEPSS rescore
  19. 2026-06-07 17:46 UTCOSV refresh
  20. 2026-06-07 15:23 UTCEPSS rescore
  21. 2026-06-07 15:23 UTCEPSS rescore
  22. 2026-06-06 13:46 UTCEPSS rescore
  23. 2026-06-06 13:46 UTCEPSS rescore
  24. 2026-06-06 13:46 UTCEPSS rescore
  25. 2026-06-05 22:45 UTCEPSS rescore
  26. 2026-06-05 22:45 UTCEPSS rescore
  27. 2026-06-04 13:10 UTCEPSS rescore
  28. 2026-06-04 13:10 UTCEPSS rescore
  29. 2026-06-02 20:11 UTCEPSS rescore
  30. 2026-06-02 20:11 UTCEPSS rescore
  31. 2026-06-02 20:11 UTCEPSS rescore
  32. 2026-06-01 13:50 UTCEPSS rescore
  33. 2026-06-01 13:50 UTCEPSS rescore
  34. 2026-05-31 22:29 UTCEPSS rescore
  35. 2026-05-31 22:29 UTCEPSS rescore
  36. 2026-05-31 00:15 UTCEPSS rescore
  37. 2026-05-29 13:42 UTCEPSS rescore
  38. 2026-05-28 13:43 UTCEPSS rescore
  39. 2026-05-28 13:43 UTCEPSS rescore
  40. 2026-05-27 13:39 UTCEPSS rescore
  41. 2026-05-27 13:39 UTCEPSS rescore
  42. 2026-05-26 13:42 UTCEPSS rescore
  43. 2026-05-26 07:17 UTCEPSS rescore
  44. 2026-05-26 07:17 UTCEPSS rescore
  45. 2026-05-23 08:11 UTCEG score recompute
  46. 2026-05-23 08:11 UTCVendor advisory

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-28662?
CVE-2021-28662 is a medium vulnerability published on May 27, 2021. An issue was discovered in Squid 4.x before 4.15 and 5.x before 5.0.6. If a remote server sends a certain response header over HTTP or HTTPS, there is a denial of service. This header can plausibly occur in benign network traffic.
When was CVE-2021-28662 disclosed?
CVE-2021-28662 was first published in the National Vulnerability Database on May 27, 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-2021-28662 actively exploited?
CVE-2021-28662 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-28662?
CVE-2021-28662 has a CVSS v3 base score of 6.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.4.
How do I remediate CVE-2021-28662?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-28662, 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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