{"id":"CVE-2026-27700","aliases":["GHSA-xh87-mx6m-69f3"],"url":"https://o3.security/vulnerability/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.","published":"2026-02-25T15:01:44.681Z","modified":"2026-08-12T03:51:46.124816231Z","cvss":{"score":8.2,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"hono","fixedVersion":"4.12.2"}],"fix":{"url":"https://github.com/honojs/hono/commit/41adbf56e252c04611f8972364ac0887ae07a4c7","label":"honojs/hono@41adbf5"},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27700.json"},{"type":"ADVISORY","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":"FIX","url":"https://github.com/honojs/hono/commit/41adbf56e252c04611f8972364ac0887ae07a4c7"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:46.124816231Z"}}