CVE-2026-48710

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. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the Host header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing request.url and falls back to scope["server"] for malformed values.

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. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the Host header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing request.url and falls back to scope["server"] for malformed values.

Summary

In affected versions, 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.

Details

When a client requests http://example.com/foo, it sends:

GET /foo HTTP/1.1
Host: example.com

Affected versions reconstructed the URL by concatenating http://{host}{path} and re-parsing the result. The Host value is only valid as a uri-host [ ":" port ] per RFC 9112 §3.2, where uri-host follows the restricted host grammar of RFC 3986 §3.2.2. When it contains characters outside that grammar - notably /, ?, or # - those characters move the path/query/fragment boundaries during re-parsing, so the parsed request.url.path no longer matches the path the server actually received. For example:

GET /foo HTTP/1.1
Host: example.com/abc?bar=

reconstructs to http://example.com/abc?bar=/foo, whose parsed path is /abc - even though routing used the real path /foo. The router still dispatches to /foo and the endpoint executes, but any middleware or code that reads request.url.path sees /abc, so path-based authorization checks can be bypassed.

Impact

Any application running an affected version that relies on request.url (or request.url.path) for security-sensitive decisions is affected. The most common case is middleware that gates access to certain path prefixes based on request.url.path. Deployments fronted by a proxy or load balancer are mitigated only if that proxy rejects or normalizes the malformed Host header before forwarding and the application does not trust attacker-controlled host headers (e.g. X-Forwarded-Host) elsewhere.

Mitigation

Upgrade to a patched version, which validates the Host header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing request.url and falls back to scope["server"] for malformed values.

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. Users should upgrade to a version greater than or equal to version 1.0.1, which validates the Host header against the grammar of RFC 9112 §3.2 / RFC 3986 §3.2.2 when constructing request.url and falls back to scope["server"] for malformed values.

TuxCare rebuilt starlette to address 1 CVE. Fixed in 0.27.0.post3+tuxcare.

TuxCare rebuilt starlette to address 8 CVEs. Fixed in 0.25.0.post1+tuxcare.

TuxCare rebuilt starlette to address 1 CVE. Fixed in 0.13.6.post6+tuxcare.

The updated package fixes security vulnerabilities: Proxy-Authorization header kept across hosts. (CVE-2024-28849) Starlette vulnerable to O(n^2) DoS via Range header merging in starlette.responses.FileResponse. (CVE-2025-62727) Security restriction bypass via malformed HTTP Host header. (CVE-2026-48710)

These are all security issues fixed in the python311-starlette-1.2.0-1.1 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the python311-google-adk-2.2.0-1.1 package on the GA media of openSUSE Tumbleweed.

This update for python-starlette fixes the following issues

• CVE-2025-54121: denial-of-service when parsing a multi-part form with large files (bsc#1246855).
• CVE-2025-62727: DoS via Range header merging (bsc#1252805).
• CVE-2026-48710: Missing Host header validation poisons request.url.path, bypassing path-based security checks (bsc#1266369).

Starlette reconstructs the requested URL based on the HTTP Host request header and requested path, but does not perform any validation of the Host header value. This allows attackers to inject paths into the host part, prepending the actual path. However, routing in Starlette is based on the actual request path. This inconsistent interpretation of HTTP requests may lead to issues such as authentication bypass when the authentication depends on the reconstructed URL’s path.

Root has patched CVE-2026-48710 in the starlette package for Root:PyPI. Multiple fixed versions available.

This update for python-starlette fixes the following issues

• CVE-2025-54121: denial-of-service when parsing a multi-part form with large files (bsc#1246855).
• CVE-2025-62727: DoS via Range header merging (bsc#1252805).
• CVE-2026-48710: Missing Host header validation poisons request.url.path, bypassing path-based security checks (bsc#1266369).