CVE-2021-43848

HIGHNVD 7.47.4
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This high-severity CVE scores 7.4 under NVD CVSS v3. EPSS exploit probability: 2.7% (85th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Trending — 3 sources updated this weekElevated
7.4EG
EchelonGraph verdictPlan mitigationRemediate within your standard update timelines (the SSVC decision on this page).
  • Public exploit or proof-of-concept code is available
CISA-KEV: Not listedEPSS PROB: 2.7%CVSS: 7.4Exploit: Public PoCExposed services: Not assessed

A fix is referenced (a reference tagged "Patch", often a source commit), but no release containing it is confirmed — find the release that contains it; until it is applied, mitigate (WAF / firewall / segmentation).

h2o is an open source http server. In code prior to the 8c0eca3 commit h2o may attempt to access uninitialized memory. When receiving QUIC frames in certain order, HTTP/3 server-side implementation of h2o can be misguided to treat uninitialized memory as HTTP/3 frames that have been received. When h2o is used as a reverse proxy, an attacker can abuse this vulnerability to send internal state of h2o to backend servers controlled by the attacker or third party. Also, if there is an HTTP endpoint that reflects the traffic sent from the client, an attacker can use that reflector to obtain internal state of h2o. This internal state includes traffic of other connections in unencrypted form and TLS session tickets. This vulnerability exists in h2o server with HTTP/3 support, between commit 93af138 and d1f0f65. None of the released versions of h2o are affected by this vulnerability. There are no known workarounds. Users of unreleased versions of h2o using HTTP/3 are advised to upgrade immediately.

CVSS v3
7.4
EG Score
7.4HIGHmedium confidence
EG Risk
49
EG Risk 49/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity74% × 45%
Impact severity (EG Severity): CVSS 7.4 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it and apply that within your standard update timelines; until then, restrict network exposure of the affected system or apply the vendor's mitigation.
EPSS PROB
2.7%
EPSS %ILE
85th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (7.4): severity, escalated by confirmed exploitation. This CVE's 7.4 is its impact severity (EG Severity), not escalated.

EG Severity
7.4 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
2.7% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-20). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it and apply that within your standard update timelines; until then, restrict network exposure of the affected system or apply the vendor's mitigation.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

February 1, 2022

Last Modified

November 21, 2024

References (2)

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 37× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 95 of 200 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 5 repeat rows among the latest 100 are merged into the row they repeat. The 105 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  2. 2026-10-22 16:29 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  3. 2026-10-21 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  4. 2026-10-21 08:49 UTCEG score recompute
  5. 2026-10-20 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  6. 2026-10-19 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  7. 2026-10-18 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  8. 2026-10-18 08:52 UTCEG score recompute
  9. 2026-10-17 16:29 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  10. 2026-10-17 07:24 UTCOSV refresh
  11. 2026-10-16 16:34 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  12. 2026-10-15 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  13. 2026-10-14 16:29 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  14. 2026-10-13 16:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  15. 2026-10-12 19:08 UTCEG score recompute
  16. 2026-10-12 16:30 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  17. 2026-10-11 23:33 UTCEG score recompute
  18. 2026-10-11 13:44 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  19. 2026-10-10 19:56 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  20. 2026-10-09 20:04 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  21. 2026-10-08 16:40 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  22. 2026-10-07 23:45 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  23. 2026-10-06 15:14 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  24. 2026-10-05 17:40 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  25. 2026-10-04 23:19 UTCEPSS rescoreEPSS 2.7% · 85th percentile
Show 70 more
  1. 2026-10-03 14:22 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  2. 2026-10-02 16:23 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  3. 2026-10-01 19:46 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  4. 2026-09-30 15:43 UTCEG score recompute
  5. 2026-09-30 15:00 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  6. 2026-09-29 15:15 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  7. 2026-09-28 13:47 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  8. 2026-09-27 13:41 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  9. 2026-09-26 15:54 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  10. 2026-09-26 00:21 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  11. 2026-09-25 07:05 UTCOSV refresh
  12. 2026-09-24 14:00 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  13. 2026-09-23 13:44 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  14. 2026-09-22 14:44 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  15. 2026-09-21 20:28 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  16. 2026-09-20 20:13 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  17. 2026-09-19 15:38 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  18. 2026-09-18 19:23 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  19. 2026-09-17 19:23 UTCEPSS rescoreEPSS 2.7% · 85th percentile
  20. 2026-09-16 14:05 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  21. 2026-09-15 03:06 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  22. 2026-09-12 14:57 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  23. 2026-09-11 14:49 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  24. 2026-09-11 09:33 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  25. 2026-09-08 21:56 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  26. 2026-09-07 15:58 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  27. 2026-09-06 13:45 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  28. 2026-09-05 22:21 UTCOSV refresh
  29. 2026-09-05 15:25 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  30. 2026-09-04 13:57 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  31. 2026-09-04 05:03 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  32. 2026-09-02 14:09 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  33. 2026-09-01 13:50 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  34. 2026-09-01 03:33 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  35. 2026-08-30 19:14 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  36. 2026-08-30 01:19 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  37. 2026-08-28 21:37 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  38. 2026-08-27 14:22 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  39. 2026-08-26 14:43 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  40. 2026-08-25 13:46 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  41. 2026-08-24 14:13 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  42. 2026-08-23 00:16 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  43. 2026-08-21 23:46 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  44. 2026-08-20 22:52 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  45. 2026-08-19 17:01 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  46. 2026-08-19 09:29 UTCOSV refresh
  47. 2026-08-18 13:45 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  48. 2026-08-17 13:44 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  49. 2026-08-16 14:53 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  50. 2026-08-16 02:11 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  51. 2026-08-15 01:27 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  52. 2026-08-13 21:57 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  53. 2026-08-12 13:48 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  54. 2026-08-11 13:38 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  55. 2026-08-08 16:33 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  56. 2026-08-07 16:24 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  57. 2026-08-06 13:44 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  58. 2026-08-05 19:14 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  59. 2026-08-04 10:34 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  60. 2026-08-04 04:57 UTCOSV refresh
  61. 2026-08-03 10:33 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  62. 2026-08-02 02:24 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  63. 2026-08-01 04:13 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  64. 2026-07-30 16:25 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  65. 2026-07-30 01:28 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  66. 2026-07-28 15:33 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  67. 2026-07-26 14:52 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  68. 2026-07-25 14:15 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  69. 2026-07-24 14:15 UTCEPSS rescoreEPSS 2.7% · 84th percentile
  70. 2026-07-23 14:16 UTCEPSS rescoreEPSS 2.7% · 84th percentile

Publicly available exploits

(1 reference)

Public exploit code is referenced for this CVE (1 GitHub PoC). No release with the fix is confirmed, so defenders should restrict or isolate affected systems accordingly until one is applied.

  • GitHub PoCneex/hui2ochko
    Published Feb 3, 2022

    exploit for CVE-2021-43848

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-43848?
CVE-2021-43848 is a high-severity vulnerability; its CVE record was published on February 1, 2022. h2o is an open source http server. In code prior to the 8c0eca3 commit h2o may attempt to access uninitialized memory. When receiving QUIC frames in certain order, HTTP/3 server-side implementation of h2o can be misguided to treat uninitialized memory as HTTP/3 frames that have been received. When…
When was the CVE record for CVE-2021-43848 published?
The CVE record for CVE-2021-43848 was published on February 1, 2022. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 21, 2024; the record at its source may have been updated since.
Is CVE-2021-43848 actively exploited?
CVE-2021-43848 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 2.7% probability of exploitation in the next 30 days (85th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-43848?
CVE-2021-43848 has a CVSS v3 base score of 7.4 (NVD).
How do I remediate CVE-2021-43848?
A fix for CVE-2021-43848 is referenced (a reference tagged "Patch", often a source commit), but EchelonGraph has no release containing it on record. Check that reference and the vendor's advisory for a release that contains the fix and update to it; until then, restrict network exposure of the affected system or apply the vendor's mitigation.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2021-43848

Explore →

Is Your Infrastructure Affected by CVE-2021-43848?

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

Book a Demo →Browse All CVEs