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Vulnerabilities

Vulnerability · CVE-2026-27959

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

Published Feb 26, 2026 · catalog updated Jul 15, 2026 · Koa is middleware for

Check if you run it

No confirmed exploitation is on record for CVE-2026-27959. EPSS is 0.53%. Act only if a listed version of Koa is middleware for is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Koa is middleware for).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.53%
Remediation
Advisory link
Affected products
cpe koajs/koa

Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's 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, returns - an attacker-controlled value. Applications using 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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe koajs/koaversion unspecified

How to fix CVE-2026-27959

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-27959. EPSS is 0.53%. Act only if a listed version of Koa is middleware for is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-20: Improper Input Validation. EPSS 0.53%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Feb 26, 2026 · NIST NVD

    Detected

    Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's 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, returns - an attacker-controlled value. Applications using for URL gener

  2. Jul 15, 2026 · NIST NVD

    Updated

    Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's 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, returns - an attacker-controlled value. Applications using for URL gener

Sources

  • CVE.orgVulnerability recordCVE-2026-27959

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-27959

    30-day exploitation probability 0.5%

    first.org
  • NIST NVDVulnerability recordCVE-2026-27959

    Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's 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.

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.