---
id: CVE-2026-48818
aliases:
  - GHSA-wqp7-x3pw-xc5r
  - PYSEC-2026-2281
title: >-
  Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on
  Windows
summary: >-
  Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on
  Windows
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'
vendor: starlette
product: starlette
ecosystem: pip
affected:
  - starlette < 1.1.0
patched:
  - starlette 1.1.0
published: '2026-06-15'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:51.079936646Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-wqp7-x3pw-xc5r'
references:
  - url: >-
      https://github.com/Kludex/starlette/security/advisories/GHSA-wqp7-x3pw-xc5r
  - url: 'https://github.com/Kludex/starlette'
  - url: 'https://github.com/advisories/GHSA-wqp7-x3pw-xc5r'
tags:
  - osv
  - pip
  - ghsa
epss: 0.00368
epssPercentile: 0.30656
cwe:
  - CWE-918
ingestedAt: '2026-07-07T15:41:58.661Z'
---

## Overview

### Summary

When serving static files on Windows, `StaticFiles` resolves the requested path with [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath). If a UNC path (such as `\\attacker.com\share`) reaches the resolver, `realpath` causes the process to open a connection to the remote host over SMB (port 445). This is a server-side request forgery (SSRF) that leaks the service account's NTLMv2 credentials to the attacker-controlled host, which can then be cracked offline or relayed to other hosts.

### Details

`StaticFiles.lookup_path()` joins the requested path onto the served directory and calls [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath) on the result before checking containment with [`os.path.commonpath`](https://docs.python.org/3/library/os.path.html#os.path.commonpath). On Windows, a UNC path is absolute, so [`os.path.join`](https://docs.python.org/3/library/os.path.html#os.path.join) discards the served directory and `realpath` resolves the bare UNC path, triggering the outbound SMB connection and NTLM authentication before the containment check rejects the path. The HTTP response is a benign 404, but the credential disclosure has already happened. POSIX systems are not affected.

This only affects the default configuration (`follow_symlink=False`), which uses [`os.path.realpath`](https://docs.python.org/3/library/os.path.html#os.path.realpath). The `follow_symlink=True` branch uses [`os.path.abspath`](https://docs.python.org/3/library/os.path.html#os.path.abspath), which performs no I/O.

### Impact

Applications running on Windows that serve files with `StaticFiles` (directly, or via a framework built on Starlette such as FastAPI) in the default configuration are affected. `StaticFiles` is typically unauthenticated, so any client can trigger the SMB connection and leak the service account's NTLMv2 hash. A secondary impact is discovering internal hosts reachable over SMB by timing responses for valid versus invalid addresses.

### Mitigation

Applications not running on Windows are not affected. On Windows, serving static files through a dedicated web server (such as nginx or IIS) instead of `StaticFiles` avoids the issue. Blocking outbound SMB (port 445) from the application host prevents the credential disclosure even if a UNC path is resolved.

## Affected packages

- `starlette < 1.1.0`

## Remediation

Upgrade to a patched release:

- `starlette 1.1.0`