---
id: CVE-2026-54287
aliases:
  - GHSA-j6c9-x7qj-28xf
title: >-
  hono: AWS Lambda adapter merges multiple `Set-Cookie` headers into one value,
  dropping cookies on ALB single-header and Lattice
summary: >-
  hono: AWS Lambda adapter merges multiple `Set-Cookie` headers into one value,
  dropping cookies on ALB single-header and Lattice
severity: medium
cvss: 5.3
cwe:
  - CWE-116
vendor: hono
product: hono
ecosystem: npm
affected:
  - hono < 4.12.25
patched:
  - hono 4.12.25
published: '2026-06-16'
updated: '2026-06-16'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-j6c9-x7qj-28xf'
references:
  - url: 'https://github.com/honojs/hono/security/advisories/GHSA-j6c9-x7qj-28xf'
  - url: 'https://github.com/advisories/GHSA-j6c9-x7qj-28xf'
tags:
  - ghsa
  - npm
epss: 0.0031
epssPercentile: 0.21411
ingestedAt: '2026-07-07T15:41:58.362Z'
---

## Overview

### Summary

On AWS Lambda, the ALB single-header response and the VPC Lattice v2 response join multiple `Set-Cookie` headers into one comma-separated value. Because commas also appear inside cookie attributes (for example `Expires` dates), clients cannot split the value back into individual cookies and silently drop or misparse them.

### Details

Per RFC 6265, each cookie must be its own `Set-Cookie` header line, and commas may appear inside attribute values. Joining cookies with `", "` collides with those commas, producing a value that clients cannot reliably split. Only ALB single-header mode and VPC Lattice v2 are affected; API Gateway v1/v2 and ALB with multi-value headers enabled already use an array and are unaffected.

### Impact

A client may receive only one of the cookies, a malformed cookie, or none. Session, CSRF, or preference cookies can silently fail to apply, breaking sessions or forcing re-authentication. This affects applications that set multiple cookies per response and run on AWS Lambda behind an ALB in single-header mode (the default) or VPC Lattice v2.

## Affected packages

- `hono < 4.12.25`

## Remediation

Upgrade to a patched release:

- `hono 4.12.25`