CVE-2026-48818
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk29th percentile - higher than 29% of all known CVEs
Summary
A vulnerability in Starlette 1.0.1 and earlier on Windows allows SSRF via UNC paths. When the server validates the path, it sends an SMB request to the attacker, leaking NTLMv2 credentials. The issue affects default follow_symlink=False deployments, including frameworks like FastAPI.
Risk Assessment
An attacker can capture and crack the NTLMv2 credentials of the service account, leading to unauthorized access to network resources or relay attacks. Credentials are leaked even if the HTTP response is a 404.
Recommendation
Upgrade Starlette to version 1.1.0 or later immediately. If an upgrade is not possible, consider disabling static file handling on Windows or implementing network-level controls to block outbound SMB traffic.
Other vulnerabilities in Starlette
See all- CVE-2026-48710Medium
Starlette is a lightweight ASGI framework/toolkit. Prior to version 1.0.1, the HTTP Host request header was not validated before being used to reconstruct request.url. Because the routing algorithm relies on the raw HTTP path while request.url is rebuilt from the Host header, a malformed header could make request.url.path differ from the path that was actually requested. Middleware and endpoints that apply security restrictions based on request.url (rather than the raw scope path) could therefore be bypassed.
- CVE-2023-30798High
The vulnerability in the Starlette Python framework before version 0.25.0 allows an unauthenticated remote attacker to specify an arbitrary number of form fields or files, causing excessive memory usage and denial of service (DoS) of the HTTP service.
Original NVD description (English source)
Starlette is a lightweight ASGI framework/toolkit. In versions 1.0.1 and earlier, StaticFiles on Windows is vulnerable to SSRF. An UNC path such as \\attacker.com\share can cause os.path.realpath to initiate an outbound SMB connection before the path is rejected, exposing the service account’s NTLMv2 credentials for offline cracking or relay even though the HTTP response is only a 404. The issue affects default follow_symlink=False deployments, including frameworks built on Starlette such as FastAPI; POSIX systems and follow_symlink=True are unaffected. The issue is fixed in 1.1.0.