CVE-2026-27959: koajs koa · Improper Input Validation
Affects koajs koaSource CVE Database V5
Not known to be exploited · CVSS 7.5 High : upgrade to 3.1.2 or 2.16.4 soon.
Data as of 30 Oct 2026, 11:52 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 33% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 3.1.2, 2.16.4
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 26 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), GitHub proofs of concept, the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.
What to do
Upgrade koajs koa to 3.1.2 or 2.16.4.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| koajskoa | Affected
| Fixed in
|
| koajskoa | Affected
| Fixed in
|
npmkoapkg:npm/koaOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix is available in Koa versions 2.16.4 and 3.1.2. Users should upgrade to at least these versions to remediate the vulnerability. No additional vendor advisory indicates alternative mitigations or that no action is required.
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.
References
- github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm (opens in a new tab)
- github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df (opens in a new tab)
- github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-27959 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2442928 (opens in a new tab)
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27959.json (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:10184 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:7249 (opens in a new tab)