CVE-2026-59897Network attack vector

Security decision manipulation via substring header de-duplication

Published Jul 8, 2026 · Updated Jul 8, 2026

Header-processing error in Hono 4.3.3 through 4.12.26 allows remote attackers to alter decisions via repeated request headers. The AWS API Gateway v1 and VPC Lattice adapters use substring matching when de-duplicating sanitized values, so a value contained within another is omitted before middleware receives the request. Exploitation requires repeated values with a substring relationship and affects only applications whose security, routing, rate-limiting, or logging decisions depend on the complete header list.

CVSS severity4.8
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Header-processing error in Hono 4.3.3 through 4.12.26 allows remote attackers to alter decisions via repeated request headers. The AWS API Gateway v1 and VPC Lattice adapters use substring matching when de-duplicating sanitized values, so a value contained within another is omitted before middleware receives the request. Exploitation requires repeated values with a substring relationship and affects only applications whose security, routing, rate-limiting, or logging decisions depend on the complete header list.

The record

CVE
CVE-2026-59897
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
Hono
Product
Hono
Classifications
CWE-348, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 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=>= 4.3.3, < 4.12.27

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Hono · Honoversion=>= 4.3.3, < 4.12.27

Published CVSS scores

4.8GitHub, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

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-348Use of Less Trusted Source
T1190Exploit Public-Facing Application

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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