hono: AWS Lambda adapter merges multiple `Set-Cookie` headers into one value, dropping cookies on ALB single-header and Lattice
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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | hono | < 4.12.25 | 4.12.25 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-116- Platform
- npm
- Package
hono- Disclosed
- 16.06.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-j6c9-x7qj-28xf - CC BY 4.0
Vulnerability history: hono
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 52
- First → latest
- 12.2023 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 7
- Medium 41
- Low 4
Disclosures per year
- 2023: 1
- 2024: 3
- 2025: 4
- 2026: 44
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hono: AWS Lambda adapter merges multiple `Set-Cookie` headers into one value, dropping cookies on ALB single-header and Lattice this entry
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