CVE-2026-54287Network attack vector

Cookie loss via comma-joined Set-Cookie headers

Published Jun 22, 2026 · Updated Jun 22, 2026

Output encoding error in Hono before 4.12.25 allows remote attackers to make clients drop or misparse cookies in AWS Lambda responses. The AWS Lambda adapter joins separate Set-Cookie fields with commas for ALB single-header and VPC Lattice v2 responses, colliding with commas inside attributes such as Expires. Exposure requires multiple cookies per response behind an ALB in default single-header mode or VPC Lattice v2; session, CSRF, or preference cookies can fail.

CVSS severity5.3
Medium
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Output encoding error in Hono before 4.12.25 allows remote attackers to make clients drop or misparse cookies in AWS Lambda responses. The AWS Lambda adapter joins separate Set-Cookie fields with commas for ALB single-header and VPC Lattice v2 responses, colliding with commas inside attributes such as Expires. Exposure requires multiple cookies per response behind an ALB in default single-header mode or VPC Lattice v2; session, CSRF, or preference cookies can fail.

The record

CVE
CVE-2026-54287
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
Hono
Product
Hono
Classifications
CWE-116
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 22, 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=< 4.12.25

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Hono · Honoversion=< 4.12.25

Published CVSS scores

5.3GitHubCVSS: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.

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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-116Improper Encoding or Escaping of Output

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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