PT-2026-22104 · Koa · Koa

P80N-Sec · Published 2026-02-26 · Updated 2026-03-03 · CVE-2026-27959

Positive Technologies (AI Summary)

CVSS v3.1

7.5

High

Base vector

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Name of the Vulnerable Software and Affected Versions Koa versions prior to 3.1.2 Koa versions prior to 2.16.4

Description Koa middleware for Node.js, using ES2017 async functions, has an issue where the ctx.hostname API improperly parses the HTTP Host header. The parsing does not validate input against RFC 3986 hostname syntax, specifically failing to properly handle colons. A malformed Host header containing an @ symbol can result in ctx.hostname returning an attacker-controlled value, such as evil[.]com. Applications utilizing ctx.hostname for URL generation, password reset links, email verification URLs, or routing decisions are susceptible to Host header injection attacks. The ctx.hostname API endpoint is vulnerable. The Host header is a vulnerable parameter.

Recommendations Update to Koa version 3.1.2 or later. Update to Koa version 2.16.4 or later.

Exploit

Fix

RCE

Special Elements Injection

Weakness Enumeration

CWE-20

CWE-74

Related Identifiers

CVE-2026-27959

GHSA-7GCC-R8M5-44QM

Affected Products

Koa

References · 13

• 🔥 https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27959.json · Exploit
• https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb · Patch
• https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df · Patch
• https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-7gcc-r8m5-44qm · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2026-27959 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-27959 · Security Note
• https://github.com/koajs/koa · Note
• https://twitter.com/CVEnew/status/2027004213738233990 · Twitter Post
• https://t.me/CVEtracker/45807 · Telegram Post
• https://twitter.com/cracbot/status/2028787642666787271 · Twitter Post
• https://twitter.com/VulmonFeeds/status/2026962746160357833 · Twitter Post
• https://twitter.com/_cvereports/status/2027212166550479242 · Twitter Post