GHSA-XH87-MX6M-69F3
Vulnerability from github – Published: 2026-02-25 18:02 – Updated: 2026-02-27 20:55Summary
When using the AWS Lambda adapter (hono/aws-lambda) behind an Application Load Balancer (ALB), the getConnInfo() function incorrectly selected the first value from the X-Forwarded-For header.
Because AWS ALB appends the real client IP address to the end of the X-Forwarded-For header, the first value can be attacker-controlled.
This could allow IP-based access control mechanisms (such as the ipRestriction middleware) to be bypassed.
Details
In ALB environments, AWS appends the actual client IP address to the end of any existing X-Forwarded-For header value. However, the previous implementation of getConnInfo() extracted the leftmost IP address:
address = xff.split(',')[0].trim()
If a client sent:
X-Forwarded-For: <spoofed-ip>
ALB would forward:
X-Forwarded-For: <spoofed-ip>, <real-client-ip>
Since the implementation selected the first value, the spoofed IP address was trusted. This affected applications using:
ipRestriction(getConnInfo, { allowList: [...] })
or any custom middleware relying on getConnInfo(c).remote.address for authorization decisions.
The issue only affects deployments using the AWS Lambda adapter behind an ALB. API Gateway (v1/v2) and Lambda Function URLs are not affected, as they use AWS-provided source IP values from requestContext.
Impact
An unauthenticated remote attacker could bypass IP-based access restrictions by supplying a crafted X-Forwarded-For header. This may allow access to resources that were intended to be restricted by IP address.
Only applications deployed behind an ALB and relying on getConnInfo() for IP-based authorization are affected.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "hono"
},
"ranges": [
{
"events": [
{
"introduced": "4.12.0"
},
{
"fixed": "4.12.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-27700"
],
"database_specific": {
"cwe_ids": [
"CWE-290",
"CWE-345"
],
"github_reviewed": true,
"github_reviewed_at": "2026-02-25T18:02:19Z",
"nvd_published_at": "2026-02-25T16:23:26Z",
"severity": "HIGH"
},
"details": "## Summary\n\nWhen using the AWS Lambda adapter (`hono/aws-lambda`) behind an Application Load Balancer (ALB), the `getConnInfo()` function incorrectly selected the first value from the `X-Forwarded-For` header.\n\nBecause AWS ALB appends the real client IP address to the end of the `X-Forwarded-For` header, the first value can be attacker-controlled.\n\nThis could allow IP-based access control mechanisms (such as the `ipRestriction` middleware) to be bypassed.\n\n## Details\n\nIn ALB environments, AWS appends the actual client IP address to the end of any existing `X-Forwarded-For` header value. However, the previous implementation of `getConnInfo()` extracted the leftmost IP address:\n\n```ts\naddress = xff.split(\u0027,\u0027)[0].trim()\n```\n\nIf a client sent:\n\n```\nX-Forwarded-For: \u003cspoofed-ip\u003e\n```\n\nALB would forward:\n\n```\nX-Forwarded-For: \u003cspoofed-ip\u003e, \u003creal-client-ip\u003e\n```\n\nSince the implementation selected the first value, the spoofed IP address was trusted. This affected applications using:\n\n```ts\nipRestriction(getConnInfo, { allowList: [...] })\n```\n\nor any custom middleware relying on `getConnInfo(c).remote.address` for authorization decisions.\n\nThe issue only affects deployments using the AWS Lambda adapter behind an ALB. API Gateway (v1/v2) and Lambda Function URLs are not affected, as they use AWS-provided source IP values from `requestContext`.\n\n## Impact\n\nAn unauthenticated remote attacker could bypass IP-based access restrictions by supplying a crafted `X-Forwarded-For` header. This may allow access to resources that were intended to be restricted by IP address.\n\nOnly applications deployed behind an ALB and relying on `getConnInfo()` for IP-based authorization are affected.",
"id": "GHSA-xh87-mx6m-69f3",
"modified": "2026-02-27T20:55:22Z",
"published": "2026-02-25T18:02:19Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/honojs/hono/security/advisories/GHSA-xh87-mx6m-69f3"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27700"
},
{
"type": "WEB",
"url": "https://github.com/honojs/hono/commit/41adbf56e252c04611f8972364ac0887ae07a4c7"
},
{
"type": "PACKAGE",
"url": "https://github.com/honojs/hono"
},
{
"type": "WEB",
"url": "https://github.com/honojs/hono/releases/tag/v4.12.2"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo"
}
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