Security readout for executives and security teams
Plain-English summary
Fastify applications using @fastify/middie before 9.1.0 may fail to run path-specific middleware when a request uses URL-encoded characters. If that middleware enforces authentication or other controls, protected routes could be reached without those checks. The vendor fixed this in 9.1.0.
Executive priority
Treat as a high-priority application dependency update for Fastify services protecting routes with middleware. Business urgency is highest for externally reachable APIs and admin endpoints. No active exploitation evidence is provided, but the impact can include bypassing intended access controls.
Technical view
@fastify/middie matched middleware prefixes against an encoded path, while Fastify routing decoded the path before selecting a handler. This mismatch lets encoded path variants bypass middleware registered for a specific prefix. The CVE lists CVSS 8.4, CWE-177, affected versions before 9.1.0, and a fix in 9.1.0.
Likely exposure
Exposure is likely limited to Node.js Fastify services that use @fastify/middie versions below 9.1.0 and rely on path-prefix middleware for security checks, logging, rate limits, or request constraints.
Exploitation context
The CVSS vector indicates network reachability, low privileges, no user interaction, high attack complexity, and possible confidentiality and integrity impact. The source bundle does not show CISA KEV listing or cited evidence of active exploitation.
Researcher notes
Focus analysis on path normalization differences between middleware matching and Fastify route matching. The advisory states encoded paths can skip middleware while still reaching decoded route handlers. Do not assume all Fastify apps are affected; exposure depends on @fastify/middie usage and security reliance on prefixed middleware.
Mitigation direction
- Upgrade @fastify/middie to version 9.1.0 or later.
- Prioritize services where prefix middleware enforces authentication or authorization.
- Review vendor advisory and release notes for any additional guidance.
- Redeploy and restart affected services after dependency updates.
- Check transitive dependency paths that may include vulnerable @fastify/middie versions.
Validation and detection
- Inventory Fastify applications and dependency manifests for @fastify/middie versions below 9.1.0.
- Identify middleware registered with specific path prefixes.
- Confirm security-critical middleware still executes for encoded path variants in staging.
- Verify production builds use @fastify/middie 9.1.0 or later.
- Review access logs for unusual encoded requests to protected route prefixes.
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 lookupCVE-2026-22031 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/middie/security/advisories/GHSA-cxrg-g7r8-w69pCVE reference · x_refsource_CONFIRM
- https://github.com/fastify/middie/pull/245CVE reference · x_refsource_MISC
- https://github.com/fastify/middie/commit/d44cd56eb724490babf7b452fdbbdd37ea2effbaCVE reference · x_refsource_MISC
- https://github.com/fastify/middie/releases/tag/v9.1.0CVE 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.