CVE-2021-31618

HIGHNVD 7.58.1▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.1 because EPSS predicts 51% probability of exploitation within the next 30 days (top 1.2% of all CVEs). NVD baseline CVSS 7.5 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, ghsa, nvd
Trending — 3 sources updated this weekElevated
7.5
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 51%
CISA-KEV: Not listedEPSS: 51%CVSS: 7.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Apache HTTP Server protocol handler for the HTTP/2 protocol checks received request headers against the size limitations as configured for the server and used for the HTTP/1 protocol as well. On violation of these restrictions and HTTP response is sent to the client with a status code indicating why the request was rejected. This rejection response was not fully initialised in the HTTP/2 protocol handler if the offending header was the very first one received or appeared in a a footer. This led to a NULL pointer dereference on initialised memory, crashing reliably the child process. Since such a triggering HTTP/2 request is easy to craft and submit, this can be exploited to DoS the server. This issue affected mod_http2 1.15.17 and Apache HTTP Server version 2.4.47 only. Apache HTTP Server 2.4.47 was never released.

CVSS v3
7.5
EG Score
8.1(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
Severity81% × 45%
Exploitation51% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
98.8%
KEV
Not listed

Published

June 15, 2021

Last Modified

November 21, 2024

References (26)

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 12× 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. 2026-07-24 14:15 UTCEPSS rescore
  2. 2026-07-23 14:16 UTCEPSS rescore
  3. 2026-07-23 14:16 UTCEPSS rescore
  4. 2026-07-23 02:00 UTCEG score recompute▲ 0.60
  5. 2026-07-22 22:47 UTCEG score recompute
  6. 2026-07-22 14:06 UTCEPSS rescore
  7. 2026-07-22 14:06 UTCEPSS rescore
  8. 2026-07-21 15:22 UTCEPSS rescore
  9. 2026-07-21 15:22 UTCEPSS rescore
  10. 2026-07-20 17:05 UTCEPSS rescore
  11. 2026-07-19 02:27 UTCEPSS rescore
  12. 2026-07-18 18:29 UTCOSV refresh
  13. 2026-07-16 17:00 UTCEPSS rescore
  14. 2026-07-16 17:00 UTCEPSS rescore
  15. 2026-07-15 16:55 UTCEPSS rescore
  16. 2026-07-13 22:27 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. 2026-07-08 15:12 UTCEPSS rescore
  22. 2026-07-06 02:21 UTCEPSS rescore
  23. 2026-07-04 06:29 UTCEPSS rescore
  24. 2026-07-04 06:29 UTCEPSS rescore
  25. 2026-07-01 15:04 UTCEPSS rescore
Show 55 more
  1. 2026-07-01 01:18 UTCOSV refresh
  2. 2026-06-30 23:20 UTCEPSS rescore
  3. 2026-06-30 23:20 UTCEPSS rescore
  4. 2026-06-28 04:54 UTCEPSS rescore
  5. 2026-06-28 04:54 UTCEPSS rescore
  6. 2026-06-27 03:06 UTCEPSS rescore
  7. 2026-06-25 13:48 UTCEPSS rescore
  8. 2026-06-25 13:48 UTCEPSS rescore
  9. 2026-06-24 14:03 UTCEPSS rescore
  10. 2026-06-24 14:03 UTCEPSS rescore
  11. 2026-06-23 21:31 UTCEPSS rescore
  12. 2026-06-23 21:31 UTCEPSS rescore
  13. 2026-06-21 01:58 UTCEPSS rescore
  14. 2026-06-21 01:58 UTCEPSS rescore
  15. 2026-06-18 17:51 UTCEPSS rescore
  16. 2026-06-18 17:51 UTCEPSS rescore
  17. 2026-06-17 17:51 UTCEPSS rescore
  18. 2026-06-16 17:51 UTCEPSS rescore
  19. 2026-06-16 17:51 UTCEPSS rescore
  20. 2026-06-15 17:46 UTCEPSS rescore
  21. 2026-06-13 22:58 UTCEPSS rescore
  22. 2026-06-13 22:58 UTCEPSS rescore
  23. 2026-06-13 03:38 UTCOSV refresh
  24. 2026-06-12 23:10 UTCEPSS rescore
  25. 2026-06-12 23:10 UTCEPSS rescore
  26. 2026-06-11 13:58 UTCEPSS rescore
  27. 2026-06-10 22:16 UTCEPSS rescore
  28. 2026-06-10 13:20 UTCEPSS rescore
  29. 2026-06-07 15:23 UTCEPSS rescore
  30. 2026-06-07 15:23 UTCEPSS rescore
  31. 2026-06-05 22:45 UTCEPSS rescore
  32. 2026-06-05 22:45 UTCEPSS rescore
  33. 2026-06-05 06:09 UTCEPSS rescore
  34. 2026-06-05 06:09 UTCEPSS rescore
  35. 2026-06-04 13:10 UTCEPSS rescore
  36. 2026-06-04 13:10 UTCEPSS rescore
  37. 2026-06-02 20:11 UTCEPSS rescore
  38. 2026-06-02 20:11 UTCEPSS rescore
  39. 2026-06-02 20:11 UTCEPSS rescore
  40. 2026-06-01 13:50 UTCEPSS rescore
  41. 2026-06-01 13:50 UTCEPSS rescore
  42. 2026-05-31 22:29 UTCEPSS rescore
  43. 2026-05-31 22:29 UTCEPSS rescore
  44. 2026-05-31 00:15 UTCEPSS rescore
  45. 2026-05-29 13:42 UTCEPSS rescore
  46. 2026-05-28 13:43 UTCEPSS rescore
  47. 2026-05-28 13:43 UTCEPSS rescore
  48. 2026-05-27 13:39 UTCEPSS rescore
  49. 2026-05-27 13:39 UTCEPSS rescore
  50. 2026-05-26 14:54 UTCEG score recompute
  51. 2026-05-26 14:54 UTCVendor advisory
  52. 2026-05-26 14:54 UTCGHSA enrichment
  53. 2026-05-26 13:42 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-2021-31618?
CVE-2021-31618 is a high vulnerability published on June 15, 2021. Apache HTTP Server protocol handler for the HTTP/2 protocol checks received request headers against the size limitations as configured for the server and used for the HTTP/1 protocol as well. On violation of these restrictions and HTTP response is sent to the client with a status code indicating…
When was CVE-2021-31618 disclosed?
CVE-2021-31618 was first published in the National Vulnerability Database on June 15, 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-2021-31618 actively exploited?
CVE-2021-31618 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 98.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-31618?
CVE-2021-31618 has a CVSS v3 base score of 7.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.1.
How do I remediate CVE-2021-31618?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-31618, 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.

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