h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying to copy the hostname, assuming that it is NULL-terminated. This is a potential denial-of-service attack vector in sense that it might trigger segmentation violation. This issue has been fixed by commit 8dc37cb.
CVE-2026-44452
“—” beside the score: it is equal to the CVSS score beside it.
This medium-severity CVE scores 5.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4% (35th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.
Also known asEUVD-2026-45073 (ENISA EUVD)Source: ENISA EUVD
- Lower severity and no public exploit yet
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).
- CVSS v3
- 5.9
- EG Score
- 5.9MEDIUMmedium confidence
- EG Risk
- 27EG Risk 27/100
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)Severity59% × 45%Impact severity (EG Severity): CVSS 5.9 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation0.4% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.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
- 0.4%
- EPSS %ILE
- 35th
- 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 (5.9): severity, escalated by confirmed exploitation. This CVE's 5.9 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.9 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
- EG Likelihood
- 0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-24). 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
July 16, 2026
Last Modified
August 6, 2026
Advisory Details (1)
Auto-updated Jul 16, 2026heap overrun · Advisory · h2o/h2o · GitHub
https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvqAffected Packages
(2 across 2 ecosystems)
Debian:11(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| h2o | 2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (10 versions) |
| — |
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| h2o | 2.2.5+dfsg2-10 ... 2.2.5+dfsg2-9 (7 versions) |
| — |
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 9× in last 7d / 36× 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 100 of 145 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. None are among the latest 100 rows. The 45 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-10-25 14:27 UTCEG score recompute
- 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-22 23:48 UTCEG score recompute
- 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-18 03:39 UTCEG score recompute
- 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-16 16:42 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-12 16:05 UTCEG score recompute
- 2026-10-11 19:47 UTCEG score recompute
- 2026-10-11 17:01 UTCEG score recompute
- 2026-10-11 14:27 UTCEG score recompute
- 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
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- 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-10-01 11:21 UTCEG score recompute
- 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
- 2026-09-28 08:15 UTCEG score recompute
- 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
- 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
- 2026-09-24 06:36 UTCEG score recompute
- 2026-09-23 17:53 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-09-23 02:59 UTCEG score recompute
- 2026-09-20 20:15 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-09-18 09:59 UTCEG score recompute
- 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.4% · 35th percentile
- 2026-09-17 10:22 UTCEG score recompute
- 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-14 06:43 UTCEG score recompute
- 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-13 07:06 UTCEG score recompute
- 2026-09-12 15:01 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-11 21:31 UTCEG score recompute
- 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-11 09:37 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-10 09:34 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-08 22:00 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-08 00:23 UTCEG score recompute
- 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-05 20:32 UTCEG score recompute
- 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-31 03:05 UTCEG score recompute
- 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-30 03:27 UTCEG score recompute
- 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-27 12:23 UTCEG score recompute
- 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-26 07:29 UTCEG score recompute
- 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.4% · 34th percentile
- 2026-08-25 07:31 UTCEG score recompute
- 2026-08-23 07:39 UTCEG score recompute
- 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-22 08:03 UTCEG score recompute
- 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-21 08:26 UTCEG score recompute
- 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-20 08:49 UTCEG score recompute
- 2026-08-19 17:04 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-19 09:13 UTCEG score recompute
- 2026-08-18 13:48 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-18 09:35 UTCEG score recompute
- 2026-08-17 13:47 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-17 09:48 UTCEG score recompute
- 2026-08-16 14:56 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-16 10:11 UTCEG score recompute
- 2026-08-16 02:14 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-15 10:35 UTCEG score recompute
- 2026-08-15 01:30 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-14 10:59 UTCEG score recompute
- 2026-08-13 22:00 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-13 11:22 UTCEG score recompute
- 2026-08-12 13:51 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-12 11:46 UTCEG score recompute
- 2026-08-11 13:43 UTCEPSS rescoreEPSS 0.2% · 16th percentile
- 2026-08-11 12:09 UTCEG score recompute
Related CVEs(same product + same CWE)
Same product
10 shownDebian:11:h2o
- CVE-2018-0608EG 9.8EPSS p90CRITICAL
- CVE-2023-44487NVD 7.5EG 9.0 KEVEPSS p100CRITICAL
- CVE-2019-9515NVD 7.5EG 9.0EPSS p100CRITICAL
- CVE-2019-9512NVD 7.5EG 9.0EPSS p100CRITICAL
- CVE-2019-9514NVD 7.5EG 8.9EPSS p100HIGH
- CVE-2026-54340EG 7.5HIGH
- CVE-2026-44453EG 7.5HIGH
- CVE-2026-55213EG 7.5HIGH
- CVE-2025-8671EG 7.5HIGH
- CVE-2017-10908EG 7.5HIGH
Frequently asked(5)
What is CVE-2026-44452?
When was the CVE record for CVE-2026-44452 published?
Is CVE-2026-44452 actively exploited?
What is the CVSS score of CVE-2026-44452?
How do I remediate CVE-2026-44452?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-44452
Is Your Infrastructure Affected by CVE-2026-44452?
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