Node.js CVE-2026-27959
HIGH
GHSA-7gcc-r8m5-44qm
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Primary rating from Vendor (github).
CVSS VectorVendor: github
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Lifecycle Timeline
4Blast Radius
ecosystem impact- 5 npm packages depend on koa (5 direct, 0 indirect)
Ecosystem-wide dependent count for version 3.0.0.
DescriptionCVE.org
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.
AnalysisAI
Host header injection in Koa's ctx.hostname API (versions prior to 2.16.4 and 3.1.2) allows remote attackers to inject arbitrary hostnames through malformed Host headers containing @ symbols, affecting applications that use this API for security-sensitive operations like URL generation, password reset links, and email verification. Public exploit code exists for this vulnerability. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Application must use ctx.hostname API for URL generation, password reset links, email verification URLs, or routing decisions. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 7.5 (HIGH). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker could exploit this vulnerability to compromise the affected system. |
| Remediation | A vendor patch is available — apply it immediately. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all applications using Koa and determine which versions are deployed. …
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