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CVE-2026-27959 PUBLISHED CVSS 7.5 HIGH

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.

EPSS 0.12% · 30.5th percentile

Risk Scores

CVSS v3.1
7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS Score
0.12%
30.5th percentile

Affected Products

VendorProductVersions
koajskoa>= 3.0.0, < 3.1.2, < 2.16.4, 0
npmkoa3.0.0, 0, 3.0.0

Timeline

References

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