CVE-2026-48818 is a high-severity (CVSS 7.5) Server-Side Request Forgery (SSRF) vulnerability in starlette. A fix is available for starlette — see the affected versions and patch details below.
Starlette: SSRF and NTLM credential theft via UNC paths in StaticFiles on Windows
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-48818.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-48818 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,803 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
starletteReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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.lookup_path() 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 affects the default configuration (follow_symlink=False), which uses os.path.realpath. The follow_symlink=True branch uses 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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | starlette | all versions | 1.1.0pip install --upgrade 'starlette==1.1.0' |
Affected Products
starletteencodeDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for starlette, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update starlette to 1.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48818 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This Important flaw in Starlette's StaticFiles component, which allows for NTLMv2 credential theft via specially crafted UNC paths, does not affect Red Hat products. The vulnerability is specific to Windows operating systems, and the vulnerable code is not present in Red Hat's supported configurations.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for CVE-2026-48818 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat AI Inference Server 3.3 | rhaiis/vllm-spyre-rhel9:1782352919 | RHSA-2026:30087 |
| Red Hat AI Inference Server 3.3 | rhaiis/vllm-rocm-rhel9:1782353093 | RHSA-2026:30088 |
| Red Hat AI Inference Server 3.3 | rhaiis/vllm-cuda-rhel9:1782352847 | RHSA-2026:30089 |
Frequently Asked Questions
Is CVE-2026-48818 in your dependencies?
Find it across PyPI, including transitive dependencies.