CVE-2026-117518
Deferred Deferred - Pending Action

Path Traversal in Fastify Reply-From Plugin

Publication date: 2026-11-02

Last updated on: 2026-11-02

Assigner: openjs

Description
@fastify/reply-from is a Fastify plugin that forwards requests to an upstream HTTP server. In versions up to and including 12.8.0, the plugin validated proxy paths against forward-slash dot-segments only and then built the target with the WHATWG URL parser, which normalizes a backslash and its percent-encoded form to a forward slash on the http, https, ws, and wss schemes. A path that uses backslash dot-segments therefore bypasses the traversal check and resolves to a different upstream path, so an application that scopes proxying to an upstream prefix, or relies on route guards in front of the forwarding call, can have an unauthenticated request escape the intended prefix and reach other upstream endpoints. The resulting access to unintended upstream resources is primarily a confidentiality impact with limited integrity impact. The issue is fixed in @fastify/reply-from 12.8.1, where the path is normalized and any segment resolving to a single or double dot, along with control characters and ambiguous whitespace, is rejected before the URL is constructed, and users should upgrade to 12.8.1 or later. There is no workaround other than upgrading.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-11-02
Last Modified
2026-11-02
Generated
2026-11-02
AI Q&A
2026-11-02
EPSS Evaluated
N/A
NVD
CVE-2026-117518

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
@fastify/reply-from @fastify/reply-from 0

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-22 The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

This vulnerability affects the @fastify/reply-from plugin, which forwards requests to another HTTP server. Due to improper path validation, attackers can use backslash dot-segments (like %5c..%5c or raw backslashes) to bypass security checks. The plugin only checked for forward-slash dot-segments, allowing malicious paths to resolve to unintended upstream endpoints. This lets unauthenticated requests escape intended proxy prefixes and access restricted endpoints.

Detection Guidance

Check if your system uses @fastify/reply-from versions prior to 12.8.1 by running: npm list @fastify/reply-from. If the version is below 12.8.1, the system is vulnerable. Inspect proxy configurations for paths containing backslashes or dot-segments like \.. or %5c..%5c.

Impact Analysis

This vulnerability primarily impacts confidentiality by allowing unauthorized access to restricted upstream endpoints. Attackers could exploit it to read sensitive data from unintended paths. The integrity impact is limited, but the potential for data exposure is significant. Systems using @fastify/reply-from versions before 12.8.1 are at risk.

Compliance Impact

This vulnerability could lead to unauthorized data access, violating compliance requirements for data protection such as GDPR or HIPAA. Exposure of sensitive data may result in legal penalties, reputational damage, and failure to meet regulatory standards for confidentiality and access control.

Mitigation Strategies

Upgrade @fastify/reply-from to version 12.8.1 or later using: npm update @fastify/reply-from. Verify the update with npm list @fastify/reply-from. Ensure no workarounds are applied as upgrading is the only mitigation.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-117518. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart

Security Radar

News mentioning this vulnerability
Loading related security news...