CVE-2026-48060

Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. Prior to version 2.20.0, Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations. This issue has been patched in version 2.20.0.

Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. Prior to version 2.20.0, Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations. This issue has been patched in version 2.20.0.

Overview

Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations.

We used the latest Litestar version available via PyPI for this disclosure. At the time of writing, that is version 2.21.0 and we have not validated this against the current latest commit on the main branch.

Special Configurations Required

For a web application to be vulnerable to this issue, it must:

• Use templates to render the content which is returned to the user (e.g. Jinja, Mako, MiniJinja)
• Have CSRF protection enabled
• Have CSRF inputs enabled (i.e. a hidden form field which contains the CSRF token)

Links to relevant documentation for the above configurations:

• https://docs.litestar.dev/2/usage/templating.html
• https://docs.litestar.dev/latest/usage/middleware/builtin-middleware.html#csrf
• https://docs.litestar.dev/latest/usage/templating.html#adding-csrf-inputs

Reproduction Steps

1. Visit an application which contains a form, uses templating, has CSRF protection enabled, and which inserts the CSRF token as a hidden input field on forms. A proof of concept application demonstrating this configuration is included later in this disclosure for ease of reproduction.
2. Observe that the server sets the csrftoken cookie when the page loads.

<img width="1152" height="372" alt="litestar_csrf_cookie_in_browser_dev_tools" src="https://github.com/user-attachments/assets/252a5746-0f5f-4c78-9b9c-3ff4fb98e942" />

3. Set the value of the csrftoken cookie to "><h1>HTML Injection Test</h1>.

<img width="1142" height="426" alt="litestar_csrf_cookie_poisoned_with_html" src="https://github.com/user-attachments/assets/131e5015-e718-4539-8d03-969e81a34fdc" />

4. Refresh the page.
5. Observe that the contents of the cookie is rendered on the page.

<img width="1152" height="480" alt="litestar_successful_html_injection" src="https://github.com/user-attachments/assets/c997f679-7111-4620-a28d-25eabea34ca2" />

Exploit Code

There are two Proof-of-Concepts (PoC) included here. The first demonstrates that arbitrary HTML is injected into the page when the user supplies a malicious csrftoken cookie. The second demonstrates how an attacker could deliver an attack using the vulnerability to an unsuspecting user.

The proof-of-concept applications can be started using these commands:

# run poc1
python -m uvicorn poc1:app

# run poc2
python -m uvicorn poc2:app

PoC 1 - Minimum Vulnerable Application

This proof-of-concept demonstrates that a crafted csrftoken cookie will be rendered on the vulnerable page as HTML.

poc1.py

from litestar import Litestar, get, MediaType
from litestar.response import Template
from litestar.config.csrf import CSRFConfig
import jinja2, os
from pathlib import Path
from litestar import Litestar
from litestar.contrib.jinja import JinjaTemplateEngine
from litestar.template.config import TemplateConfig

@get("/")
async def hello_world() -> Template:
    return Template(
        template_name="test.jinja",
        media_type=MediaType.HTML,
    )

ENVIRONMENT = jinja2.Environment(
    loader=jinja2.FileSystemLoader(
        searchpath=os.path.join(os.path.dirname(__file__), "templates")
    ),
    autoescape=True,
)

csrf_config = CSRFConfig(secret="my_super_duper_secret")

app = Litestar(
    route_handlers=[hello_world],
    template_config=TemplateConfig(
        directory=Path("templates"),
        engine=JinjaTemplateEngine.from_environment(ENVIRONMENT),
    ),
    csrf_config=csrf_config,
)

test.jinja

<html>
    <body>
        <div>
            <form method="post">
                {{ csrf_input | safe }}
                <label for="fname">Username:</label><br>
                <input type="text"…

Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. Prior to version 2.20.0, Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations. This issue has been patched in version 2.20.0.

Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. Prior to version 2.20.0, Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations. This issue has been patched in version 2.20.0.

Overview

Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations.

We used the latest Litestar version available via PyPI for this disclosure. At the time of writing, that is version 2.21.0 and we have not validated this against the current latest commit on the main branch.

Special Configurations Required

For a web application to be vulnerable to this issue, it must:

• Use templates to render the content which is returned to the user (e.g. Jinja, Mako, MiniJinja)
• Have CSRF protection enabled
• Have CSRF inputs enabled (i.e. a hidden form field which contains the CSRF token)

Links to relevant documentation for the above configurations:

• https://docs.litestar.dev/2/usage/templating.html
• https://docs.litestar.dev/latest/usage/middleware/builtin-middleware.html#csrf
• https://docs.litestar.dev/latest/usage/templating.html#adding-csrf-inputs

Reproduction Steps

1. Visit an application which contains a form, uses templating, has CSRF protection enabled, and which inserts the CSRF token as a hidden input field on forms. A proof of concept application demonstrating this configuration is included later in this disclosure for ease of reproduction.
2. Observe that the server sets the csrftoken cookie when the page loads.

<img width="1152" height="372" alt="litestar_csrf_cookie_in_browser_dev_tools" src="https://github.com/user-attachments/assets/252a5746-0f5f-4c78-9b9c-3ff4fb98e942" />

3. Set the value of the csrftoken cookie to "><h1>HTML Injection Test</h1>.

<img width="1142" height="426" alt="litestar_csrf_cookie_poisoned_with_html" src="https://github.com/user-attachments/assets/131e5015-e718-4539-8d03-969e81a34fdc" />

4. Refresh the page.
5. Observe that the contents of the cookie is rendered on the page.

<img width="1152" height="480" alt="litestar_successful_html_injection" src="https://github.com/user-attachments/assets/c997f679-7111-4620-a28d-25eabea34ca2" />

Exploit Code

There are two Proof-of-Concepts (PoC) included here. The first demonstrates that arbitrary HTML is injected into the page when the user supplies a malicious csrftoken cookie. The second demonstrates how an attacker could deliver an attack using the vulnerability to an unsuspecting user.

The proof-of-concept applications can be started using these commands:

# run poc1
python -m uvicorn poc1:app

# run poc2
python -m uvicorn poc2:app

PoC 1 - Minimum Vulnerable Application

This proof-of-concept demonstrates that a crafted csrftoken cookie will be rendered on the vulnerable page as HTML.

poc1.py

from litestar import Litestar, get, MediaType
from litestar.response import Template
from litestar.config.csrf import CSRFConfig
import jinja2, os
from pathlib import Path
from litestar import Litestar
from litestar.contrib.jinja import JinjaTemplateEngine
from litestar.template.config import TemplateConfig

@get("/")
async def hello_world() -> Template:
    return Template(
        template_name="test.jinja",
        media_type=MediaType.HTML,
    )

ENVIRONMENT = jinja2.Environment(
    loader=jinja2.FileSystemLoader(
        searchpath=os.path.join(os.path.dirname(__file__), "templates")
    ),
    autoescape=True,
)

csrf_config = CSRFConfig(secret="my_super_duper_secret")

app = Litestar(
    route_handlers=[hello_world],
    template_config=TemplateConfig(
        directory=Path("templates"),
        engine=JinjaTemplateEngine.from_environment(ENVIRONMENT),
    ),
    csrf_config=csrf_config,
)

test.jinja

<html>
    <body>
        <div>
            <form method="post">
                {{ csrf_input | safe }}
                <label for="fname">Username:</label><br>
                <input type="text"…

Overview

Litestar instances which use a template engine in conjunction with CSRF protection are vulnerable to HTML Injection which can be escalated to Cross Site Scripting due to the contents of the CSRF cookie being excluded from automatic escaping by the template engine when configured inline with documentation recommendations.

We used the latest Litestar version available via PyPI for this disclosure. At the time of writing, that is version 2.21.0 and we have not validated this against the current latest commit on the main branch.

Special Configurations Required

For a web application to be vulnerable to this issue, it must:

• Use templates to render the content which is returned to the user (e.g. Jinja, Mako, MiniJinja)
• Have CSRF protection enabled
• Have CSRF inputs enabled (i.e. a hidden form field which contains the CSRF token)

Links to relevant documentation for the above configurations:

• https://docs.litestar.dev/2/usage/templating.html
• https://docs.litestar.dev/latest/usage/middleware/builtin-middleware.html#csrf
• https://docs.litestar.dev/latest/usage/templating.html#adding-csrf-inputs

Reproduction Steps

1. Visit an application which contains a form, uses templating, has CSRF protection enabled, and which inserts the CSRF token as a hidden input field on forms. A proof of concept application demonstrating this configuration is included later in this disclosure for ease of reproduction.
2. Observe that the server sets the csrftoken cookie when the page loads.

<img width="1152" height="372" alt="litestar_csrf_cookie_in_browser_dev_tools" src="https://github.com/user-attachments/assets/252a5746-0f5f-4c78-9b9c-3ff4fb98e942" />

3. Set the value of the csrftoken cookie to "><h1>HTML Injection Test</h1>.

<img width="1142" height="426" alt="litestar_csrf_cookie_poisoned_with_html" src="https://github.com/user-attachments/assets/131e5015-e718-4539-8d03-969e81a34fdc" />

4. Refresh the page.
5. Observe that the contents of the cookie is rendered on the page.

<img width="1152" height="480" alt="litestar_successful_html_injection" src="https://github.com/user-attachments/assets/c997f679-7111-4620-a28d-25eabea34ca2" />

Exploit Code

There are two Proof-of-Concepts (PoC) included here. The first demonstrates that arbitrary HTML is injected into the page when the user supplies a malicious csrftoken cookie. The second demonstrates how an attacker could deliver an attack using the vulnerability to an unsuspecting user.

The proof-of-concept applications can be started using these commands:

# run poc1
python -m uvicorn poc1:app

# run poc2
python -m uvicorn poc2:app

PoC 1 - Minimum Vulnerable Application

This proof-of-concept demonstrates that a crafted csrftoken cookie will be rendered on the vulnerable page as HTML.

poc1.py

from litestar import Litestar, get, MediaType
from litestar.response import Template
from litestar.config.csrf import CSRFConfig
import jinja2, os
from pathlib import Path
from litestar import Litestar
from litestar.contrib.jinja import JinjaTemplateEngine
from litestar.template.config import TemplateConfig

@get("/")
async def hello_world() -> Template:
    return Template(
        template_name="test.jinja",
        media_type=MediaType.HTML,
    )

ENVIRONMENT = jinja2.Environment(
    loader=jinja2.FileSystemLoader(
        searchpath=os.path.join(os.path.dirname(__file__), "templates")
    ),
    autoescape=True,
)

csrf_config = CSRFConfig(secret="my_super_duper_secret")

app = Litestar(
    route_handlers=[hello_world],
    template_config=TemplateConfig(
        directory=Path("templates"),
        engine=JinjaTemplateEngine.from_environment(ENVIRONMENT),
    ),
    csrf_config=csrf_config,
)

test.jinja

<html>
    <body>
        <div>
            <form method="post">
                {{ csrf_input | safe }}
                <label for="fname">Username:</label><br>
                <input type="text"…