CVE-2026-44453Network attack vector

Unauthenticated server crash via stack path allocation

Published Jul 16, 2026 · Updated Jul 16, 2026

Stack exhaustion in H2O before commit 6b5370d allows remote attackers to crash the HTTP server via crafted static-file requests. The static-file handler's on_req path builder sizes an alloca buffer from the configured real path, normalized request path, and index name. Exploitation requires a musl-based deployment whose pthread stack is smaller than the resulting allocation; the resulting guard-page fault terminates the server process.

CVSS severity7.5
High
EPSS probability0.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack exhaustion in H2O before commit 6b5370d allows remote attackers to crash the HTTP server via crafted static-file requests. The static-file handler's on_req path builder sizes an alloca buffer from the configured real path, normalized request path, and index name. Exploitation requires a musl-based deployment whose pthread stack is smaller than the resulting allocation; the resulting guard-page fault terminates the server process.

The record

CVE
CVE-2026-44453
Published
Jul 16, 2026
Updated
Jul 16, 2026
Vendor
H2O Project
Product
H2O
Classifications
CWE-789, CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 16, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 6b5370d

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

H2O Project · H2Oversion=< 6b5370d

Published CVSS scores

7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-789Memory Allocation with Excessive Size Value
CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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