Security readout for executives and security teams
Plain-English summary
CVE-2026-22037 affects Node.js applications using @fastify/express before 4.0.3. Certain protected routes can be reached without the intended middleware checks when URL-encoded characters alter path matching. This can bypass access controls or other middleware protections, depending on how the application uses path-prefixed middleware.
Executive priority
Treat as high priority for internet-facing or sensitive applications using @fastify/express. The business risk is unauthorized access to protected application functions if middleware-based controls are bypassed. Prioritize upgrade and exposure review, especially where admin or sensitive API routes rely on middleware prefixes.
Technical view
@fastify/express mishandles URL hex encoding when matching middleware registered on a path prefix. The middleware layer may not match an encoded request path, while Fastify’s router decodes and still routes to the handler. Affected versions are @fastify/express before 4.0.3. The issue is classified under CWE-177 and CWE-288 with CVSS 8.4.
Likely exposure
Exposure is limited to applications using @fastify/express versions below 4.0.3 and relying on path-prefixed middleware for authentication, authorization, filtering, logging, or other controls. Applications not using this plugin, or not depending on prefix middleware for protection, are less likely to be affected.
Exploitation context
The CVE record does not indicate known active exploitation, and it is not listed as KEV in the provided data. Exploitation requires a route/middleware design where protected handlers remain reachable even when prefix middleware is skipped. The CVSS vector indicates network access, low privileges, no user interaction, and high confidentiality and integrity impact.
Researcher notes
This issue is similar in theme to CVE-2026-22031 but affects a distinct npm module and codebase. The provided sources name 4.0.3 as patched and reference a fixing commit. Evidence is sufficient for affected version and root cause, but no public exploitation status is provided in the bundle.
Mitigation direction
- Upgrade @fastify/express to version 4.0.3 or later.
- Review package-lock, yarn.lock, pnpm-lock, and SBOM data for vulnerable versions.
- Identify routes protected primarily by path-prefixed middleware.
- Check the GitHub advisory for any updated vendor guidance.
Validation and detection
- Confirm deployed applications do not include @fastify/express below 4.0.3.
- Review middleware registrations that use path prefixes for security controls.
- Verify protected routes enforce authorization within handlers or reliably executed middleware.
- Run controlled regression tests for encoded path handling after upgrading.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-177: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-288: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2026-22037 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.4 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L1.86Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.4HighVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/fastify/fastify-express/security/advisories/GHSA-g6q3-96cp-5r5mCVE reference · x_refsource_CONFIRM
- https://github.com/fastify/fastify-express/commit/dc02a3fe1387f945143f22597baa42557d549a40CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Handling of URL Encoding (Hex Encoding)
Improper Handling of URL Encoding (Hex Encoding) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Authentication Bypass Using an Alternate Path or Channel
Authentication Bypass Using an Alternate Path or Channel represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.