Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on Windows

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

• CVE-2026-48818: 0.37% estimated exploitation activity in the next 30 days; percentile 30.71 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary When serving static files on Windows, StaticFiles resolves the requested path with 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.lookuppath() joins the requested path onto the served directory and calls os.path.realpath on the result before checking containment with os.path.commonpath. On Windows, a UNC path is absolute, so 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…

Published by the source

15 Jun 2026, 20:16 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:45 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wqp7-x3pw-xc5r

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wqp7-x3pw-xc5r

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# Patch Next advisory brief: CVE-2026-48818

Advisory: Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on Windows
IDs: CVE-2026-48818, GHSA-wqp7-x3pw-xc5r
Record: https://patchnext.com/advisories/cve-2026-48818 (revision 2, source checked 26 Oct 2026, 13:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: starlette 1.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI starlette: affected < 1.1.0; fixed in 1.1.0

## Suggested inspection (read-only)
- `python -m pip show starlette`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on starlette.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wqp7-x3pw-xc5r (OSV record GHSA-wqp7-x3pw-xc5r lists affected ranges: PyPI starlette >=0 <1.1.0 (fixed))
- Verified: https://github.com/advisories/GHSA-wqp7-x3pw-xc5r (GitHub-reviewed advisory GHSA-wqp7-x3pw-xc5r lists affected ranges: PyPI starlette >=0 <1.1.0)

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