datamodel-code-generator vulnerable to SSRF via --url: no host/IP validation, follows redirects
Summary
datamodel-code-generator's built-in HTTP fetcher (http.get_body) issues an httpx.GET against any URL passed to --url (or reached via a redirect chain) with no allow-list, no deny-list, no IP/host validation, and follow_redirects=True. Loopback addresses, RFC1918 ranges, link-local (169.254.169.254 cloud metadata), unique-local IPv6 and any other network-accessible target are all reachable. The JSON/YAML response body is parsed as a schema and reflected into the generated .py source, exfiltrating the response to anyone with access to that file (commonly committed to a repository).
Details
Sink: src/datamodel_code_generator/http.py, get_body (lines 31–61, at tag 0.60.1 / commit a321547e):
```python
def get_body(url, headers=None, ignore_tls=False,
query_parameters=None, timeout=DEFAULT_HTTP_TIMEOUT) -> str:
httpx = _get_httpx()
try:
response = httpx.get(
url,
headers=headers,
verify=not ignore_tls,
follow_redirects=True, # (A)
params=query_parameters,
timeout=timeout,
)
except Exception as e:
...
if response.status_code >= 400:
...
content_type = response.headers.get("content-type", "").lower()
if "text/html" in content_type:
raise SchemaFetchError(...) # (B) — only filter
return response.text # (C) → embedded in generated.py
```
- (A) follows redirects unconditionally — a public URL → 302 → internal address chain works.
- (B) the only filter is rejecting
text/html. Non-HTML internal endpoints (JSON APIs, cloud metadata, admin services) pass through. - (C) the response body becomes the schema; its
title, description, properties, etc. land in the generated .py as class attributes and Field(description=...) strings.
get_body is called by parser/base.py:1326 (_get_text_from_url), which is reached from CLI argument --url <URL>. (The $ref path is a separate advisory — see GHSA-D.)
Only affects users who installed the [http] extra (pip install 'datamodel-code-generator[http]').
PoC
A self-contained one-file PoC available here:
https://gist.github.com/thegr1ffyn/18de777d6c800a3b47715425e3f3e8f5
Impact
Who is impacted. Anyone who runs datamodel-codegen with a --url they didn't fully verify, or who runs it inside a network with reachable internal services. Realistic scenarios:
1. Trojan documentation / README. A blog post or README example reads datamodel-codegen --url https://schemas.example.com/user.json -o user.py. The attacker controls example.com, redirects to http://169.254.169.254/latest/meta-data/iam/security-credentials/<role>, and the IAM credentials end up as a docstring in user.py.
2. Internal port scan / disclosure. Iterating --url http://127.0.0.1:<port>/health probes localhost services; non-HTML, non-error responses confirm a service and leak its body into the generated file.
3. CI poisoning. A PR adds a Makefile rule that calls datamodel-codegen --url $(SCHEMA_URL); the CI runner reaches every internal service in its VPC and the response lands in PR artifacts.
Suggested fix. Resolve the URL host, reject loopback / private / link-local / multicast / reserved IPs by default, disable redirects by default (follow_redirects=False), re-validate after each redirect if the user opts into following them, and add an --allow-private-network flag for opt-in legitimate use.
Maintainer resolution
This report was fixed together with GHSA-954p-556p-r752 by the private security PR koxudaxi/datamodel-code-generator-ghsa-rfr2-mq9m-x2qx#1, merged into the public repository as 5fdba4a09f2d7a9996a504975b7ef7d63e3715bb. Follow-up generated-file and coverage fixes were merged in koxudaxi/datamodel-code-generator#3279 and docs were synced in #3280. The patched release is 0.61.0.
The patch hardens the shared HTTP fetcher used by both direct CLI --url fetching and remote JSON Schema/OpenAPI $ref resolution:
- validates HTTP(S) URLs before fetching;
- blocks localhost, loopback, private, link-local, reserved, and other non-public network targets by default;
- disables automatic redirect following and validates each redirect target before requesting it;
- adds
--allow-private-network / allow_private_network=True as an explicit opt-in for trusted internal schema endpoints.
Remote $ref fetching remains controlled by --allow-remote-refs; non-public/internal targets additionally require --allow-private-network.
Submitted by: Hamza Haroon (thegr1ffyn)
