---
id: GO-2026-4950
title: Authorization bypass via double-encoded paths in github.com/valyala/fasthttp
summary: Authorization bypass via double-encoded paths in github.com/valyala/fasthttp
severity: none
vendor: valyala
product: github.com/valyala/fasthttp
ecosystem: go
affected:
  - github.com/valyala/fasthttp < 1.70.0
patched:
  - github.com/valyala/fasthttp 1.70.0
published: '2026-08-18'
updated: '2026-08-19'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GO-2026-4950'
references:
  - url: 'https://github.com/golang/vulndb/issues/4950'
  - url: 'https://github.com/valyala/fasthttp/pull/2163'
  - url: 'https://gist.github.com/thesmartshadow/af53acdfe0d6ce352d14eb86cecf5a08'
  - url: 'https://github.com/valyala/fasthttp/releases/tag/v1.70.0'
tags:
  - osv
  - go
ingestedAt: '2026-08-19T19:22:24.372Z'
---

## Overview

In github.com/valyala/fasthttp before 1.70.0, ServeFile and ServeFS reinterpret filesystem paths as URIs, decoding percent-encoded sequences and treating characters like '?' and '#' as URI delimiters. In applications where authorization guards inspect ctx.Path() before passing paths to file-serving handlers, double-encoded path variants (e.g., /%2561dmin/export.csv) bypass access controls while still resolving to the protected file on disk.

## Affected packages

- `github.com/valyala/fasthttp < 1.70.0`

## Remediation

Upgrade to a patched release:

- `github.com/valyala/fasthttp 1.70.0`