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TI-2026-32393 Aliases CVE-2026-44453

h2o is vulnerable to musl libc stack overflow

Priority LOW 39CWE-770Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-770.

Summary

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00488 42nd percentileScored 2026-11-07
Fix Fixed h2o (h2o): 6b5370d

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
h2oaih2obefore 6b5370d6b5370dPatch availableCNA
  • h2o Vendorh2oai Affected before 6b5370d Fixed in 6b5370d Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:h2o:h2o:*:*:*:*:*:*:*:*before 2026-05-29Vulnerableh2oai
  • cpe:2.3:a:h2o:h2o:*:*:*:*:*:*:*:* Versions before 2026-05-29 Vulnerable ·h2oai

Remediation

  • Fix · CNA h2o (h2o) Fixed in 6b5370d

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-44453

References

Patch 1

Advisory 1

  • TI-2025-05944 Deserialization Vulnerability in h2oai/h2o-3 CVSS 3.0CRITICAL 9.8
  • TI-2024-09776 Jdbc Deserialization in h2oai/h2o-3 CVSS 3.0CRITICAL 9.8
  • TI-2024-30727 H2O.ai H2O through 3.46.0.4 allows attackers to arbitrarily set the JDBC URL, leading to… CVSS 3.1CRITICAL 9.1
  • TI-2026-03424 Remote Code Execution in h2oai/h2o-3 CVSS 3.1CRITICAL 9.8
  • TI-2024-07992 Arbitrary File Overwrite in h2oai/h2o-3 CVSS 3.0HIGH 8.2
  • TI-2023-06020 External Control of File Name or Path in h2oai/h2o-3 CVSS 3.1HIGH 8.2
See all 29 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences