CVE-2023-49803
Koajs Cross-Origin Resource Sharing For Koa ≤ 5.0.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2023-49803 is a high-severity Origin Validation Error (CWE-346) vulnerability in Koajs Cross-Origin Resource Sharing For Koa. Its CVSS base score is 8.6 (High).
Operationally, ranked at the 19th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2023-3277
Vulnerability Data
@koa/cors npm provides Cross-Origin Resource Sharing (CORS) for koa, a web framework for Node.js. Prior to version 5.0.0, the middleware operates in a way that if an allowed origin is not provided, it will return an `Access-Control-Allow-Origin` header with the…
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value of the origin from the request. This behavior completely disables one of the most crucial elements of browsers - the Same Origin Policy (SOP), this could cause a very serious security threat to the users of this middleware. If such behavior is expected, for instance, when middleware is used exclusively for prototypes and not for production applications, it should be heavily emphasized in the documentation along with an indication of the risks associated with such behavior, as many users may not be aware of it. Version 5.0.0 fixes this vulnerability.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Requires unique identification of the service before communications, addressing failures to validate the origin of the interaction.
Trusted path establishment enforces validation that the communication originates from and reaches only the intended trusted system components.
Enforces validation of the true origin of DNS responses via signatures and chain-of-trust mechanisms.
Enforces origin validation of name/address data, eliminating reliance on unverified or impersonated DNS sources.
Mandates origin validation so that only legitimate endpoints can continue the authenticated session.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Network security controls enforce origin validation at network boundaries.
Security of network services includes validating the authenticity of service endpoints.
A.8.26 requires identifying and specifying requirements for resilience against malicious attacks including SQL injections and input validation (items d, j), plus related protections (authentication, segregation, cryptography per 8.24), which can address some but not most origin validation scenarios such as those involving untrusted cross-origin requests or implicit trust in sources.
A.8.27 mandates security-by-design principles (defense-in-depth, least privilege, assume-breach, distrust-external-input, zero-trust verification) plus design reviews that can catch and block origin-validation gaps in many common cases, but leaves a bounded remainder (e.g. protocol-level or third-party component origin errors not surfaced by the organization's review process).
Secure coding practices include implementing proper origin validation to prevent spoofing.
Secure authentication verifies identity but does not address origin validation of arbitrary data flows.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-346, a class-level weakness, and none of its children carries one either.