CVE-2026-27959

HIGH EPSS 24.1%
Published Feb 26, 20264mo ago · Modified Jun 17, 20262w ago
7.5 CVSS 3.1
High
Find Similar
Published Feb 26, 2026 4mo ago
Last Modified Jun 17, 2026 2w ago

Description

Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol is received, `ctx.hostname` returns `evil[.]com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks. Versions 3.1.2 and 2.16.4 fix the issue.

CVSS Details

Base Score
7.5
Exploitability
3.9
Impact
3.6
Vector string
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality None
Integrity High
Availability None

Threat Intelligence

EPSS Exploit Probability
24.1% percentile
Exploit & Patch Status
Public Exploit Known
Patch Available

Weaknesses 1

CWE-20 Improper Input Validation Validation

Affected Products 2

VendorProductVersionRange
koajskoa* <2.16.4
koajskoa*≥3.0.0  –  <3.1.2

References 3

  • github.com https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df
    Patch
  • github.com https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb
    Patch
  • github.com https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm
    ExploitVendor Advisory

Remediation

  • github.com https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df
    Patch
  • github.com https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb
    Patch