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CVE-2026-27959

7.5 · HIGH

Koa is middleware for Node.js using ES2017 async functions.

Published Feb 26, 2026CWE-20EPSS 0.53%

Overview

CVE-2026-27959 is a high-severity vulnerability. It was published on February 26, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6dfGitHubgithub.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfebGitHubgithub.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qmRefaccess.redhat.com/errata/RHSA-2026:10184Refaccess.redhat.com/errata/RHSA-2026:7249Refaccess.redhat.com/security/cve/CVE-2026-27959Refbugzilla.redhat.com/show_bug.cgi?id=2442928Refsecurity.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27959.json

How CyberStrike helps

Frequently asked questions

What is CVE-2026-27959?

CVE-2026-27959 is a high-severity vulnerability. It was published on February 26, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-27959?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-27959?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-27959?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-27959 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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