PraisonAI: DNS rebinding bypass in `web_crawl` SSRF protection allows internal response disclosure

Issue: attacker-controlled input (urls) is validated as a string; the backend then fetches that string and re-resolves DNS independently of the guard. There is no shared, pinned IP between check and fetch.

Code point 3 — _crawl_with_httpx backend re-resolves (redirect re-validation does not stop rebinding)

Function: _crawl_with_httpx

Snippet:

with httpx.Client(follow_redirects=False, timeout=30.0) as client:
    for _ in range(max_redirects + 1):
        if not _is_safe_crawl_url(current):   # re-resolves hostname (CHECK)
            raise ValueError("Redirect target failed SSRF validation")
        response = client.get(current)        # resolves AGAIN at CONNECT

Issue: even with per-hop redirect re-validation, _is_safe_crawl_url(current) and client.get(current) are two separate DNS resolutions of the same hostname. A rebinding domain answers public to the check and internal to the connect → TOCTOU bypass. No IP pinning.

Code point 4 — urllib fallback (same function), no per-hop guard

Snippet:

import urllib.request
with urllib.request.urlopen(url, timeout=30) as response:   # re-resolves + auto-follows redirects
    content = response.read().decode('utf-8', errors='ignore')

Issue: when httpx is not installed, this fallback inside _crawl_with_httpx fetches the URL and auto-follows redirects with no per-hop/per-connect validation. (Results from this function are labelled "provider": "httpx" regardless of which path runs.)

Code point 5 — crawl4ai/Chromium backend (confirmed addendum)

The crawl4ai backend (_crawl_with_crawl4ai → crawler.arun(url=url), headless Chromium) is also runtime-confirmed affected (browser re-resolves DNS / follows redirects with no per-connect guard). To keep this report focused on the web_crawl SSRF guard, the backend-specific evidence is in SSRF-04_Crawl4AI_SSRF_Backend_Addendum.md.

Attack flow

1. Attacker controls a hostname (e.g. rebind.lab) whose authoritative DNS rebinds.
2. Lookup #1 (the guard) → a public IP → _is_safe_crawl_url() returns true.
3. The backend re-resolves → the attacker's DNS now answers an internal/private IP (cloud metadata, loopback, internal service).
4. The backend connects to the internal service and returns its body to the caller → internal data disclosure.

Why existing protection is bypassed

• The guard validates the hostname, not a pinned IP; check and connect resolve independently → DNS rebinding (TOCTOU) defeats it on every backend.
• Redirect re-validation (httpx path) re-checks the hostname but still re-resolves at connect, so it does not stop rebinding; the urllib fallback and crawl4ai backends have no per-hop guard at all.

Security boundary

The server-side fetch reaches internal/loopback/metadata services not exposed to the attacker and returns their content (CVSS Scope: Changed). Reachable wherever an agent can be induced to crawl an attacker-supplied URL (PR:L). An unauthenticated single-request path to web_crawl read-back was not found in 4.6.63 (so PR:N / Critical is not claimed).

Proof of Concept

Environment

Real PraisonAI 4.6.63 in a local Docker runtime; a controlled internal canary service (Docker-internal only, not published) returns synthetic markers; a controlled DNS responder implements rebinding for rebind.lab. No public host / real metadata / real secret. Runnable assets: PraisonAI-Runtime-Repro\runtime-files\.

Steps to reproduce

1. Burp Repeater tab PRAI-05-01-DNS-Rebind-Trigger → 127.0.0.1:18080:

POST /tool/web_crawl HTTP/1.1
Host: 127.0.0.1:18080
Content-Type: application/json

{"url":"http://rebind.lab:8081/secret"}

2. Send (PRAI-05-02-DNS-Rebind-Secret-Readback captures the response). If a send returns the "blocked" error, the rebinding DNS auto-resets (~3s) — resend.
3. Redirect variant: PRAI-05-03-Redirect-Trigger / PRAI-05-04-Redirect-Secret-Readback send {"url":"http://redirector:8082/redirect-to-internal"}.

Expected result

A safe SSRF guard refuses destinations that resolve to internal/private IPs regardless of DNS timing or redirects, and does not return internal content.

Actual result

HTTP 200 with the internal body in the crawl result. Primary evidence is the provider: "httpx" backend returning the internal canary via DNS rebinding:

{"input_url":"http://rebind.lab:8081/secret",
 "result":{"content":"{ ... \"secret\": \"PRAISONAI_INTERNAL_SECRET_CANARY_7f3a91\", \"token\": \"FAKE_INTERNAL_TOKEN_DO_NOT_USE_7f3a91\" ... }","provider":"httpx"}}

The redirect variant returns the same internal markers via a redirect chain (provider: "httpx").

Screenshots

DNS rebinding read-back

The attacker-controlled rebind.lab URL is accepted by web_crawl, and the PraisonAI response contains the internal canary response body.

DNS rebinding runtime evidence

The runtime log shows rebind.lab first resolving to an allowed/public IP during validation (guard-pass), then resolving to an internal Docker IP during the actual fetch (fetch-hit). The internal canary receives GET /secret from the PraisonAI container.

Redirect-based SSRF read-back

The attacker-controlled redirector URL is accepted by web_crawl. PraisonAI follows the redirect and returns the internal canary response body containing PRAISONAI_INTERNAL_SECRET_CANARY_7f3a91.

Redirect chain runtime evidence

The controlled redirector returns 302 -> http://internal-canary:8081/secret, and the internal canary receives GET /secret, confirming that the server-side client followed the redirect into the internal network.

Reproduction assets

The attached archive contains the local Docker runtime used to reproduce the issue with controlled canary services only. It does not contain real secrets, real cloud metadata access, or third-party API keys.

PraisonAI-Runtime-Repro.zip

Impact

SSRF against internal/loopback/cloud-metadata endpoints with disclosure of internal HTTP responses (read-back) to the attacker. Bypasses the project's SSRF protection on every fetch backend.

Suggested remediation

1. Resolve the host once, reject all returned records that are private/loopback/link-local/ULA/CGNAT/metadata, then connect to that exact validated IP (pin it; send the original Host). Do not let the HTTP client / browser re-resolve.
2. Apply the same validation + IP pinning to every backend (httpx, urllib fallback, crawl4ai) and every redirect hop.
3. Disable automatic redirect following (or cap + re-validate each hop with pinning).
4. Treat IPv4-mapped IPv6, decimal/octal/hex IPs, and CGNAT/non-global ranges as unsafe.