CVE-2026-27700: Hono Authentication Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xh87-mx6m-69f3",
  "modified" : "2026-02-27T20:55:22Z",
  "published" : "2026-02-25T18:02:19Z",
  "aliases" : [ "CVE-2026-27700" ],
  "summary" : "Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo",
  "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(',')[0].trim()\n```\n\nIf a client sent:\n\n```\nX-Forwarded-For: <spoofed-ip>\n```\n\nALB would forward:\n\n```\nX-Forwarded-For: <spoofed-ip>, <real-client-ip>\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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "hono"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.12.0"
      }, {
        "fixed" : "4.12.2"
      } ]
    } ]
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-290", "CWE-345" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-25T18:02:19Z",
    "nvd_published_at" : "2026-02-25T16:23:26Z"
  }
}