Summary
datamodel-code-generator vulnerable to SSRF protection bypass via DNS rebinding
datamodel-code-generator's anti-SSRF guard validates the resolved IP of a fetch target once and then lets httpx perform its own independent DNS resolution to connect, so the validated address is never pinned. A hostname that resolves to a public IP at validation time and a private IP at connection time (DNS rebinding) bypasses the guard and reaches loopback, link-local cloud-metadata endpoints (169.254.169.254), and other internal services, even with the default allow_private_network=False. This is a server-side request forgery reachable when the tool fetches an attacker-influenced URL (remote $ref, or --url).
Details
In src/datamodel_code_generator/http.py, get_body() calls _validate_url_for_fetch(), which resolves the host via _get_ips_from_host() (socket.getaddrinfo) and rejects non-global addresses:
ips = _get_ips_from_host(host) # resolution #1 (validation)
if not ips: return
if all(_is_safe_ip(ip) for ip in ips): return
raise SchemaFetchError(...) # blocks private/link-local/reserved
It then connects with a separate, independent resolution:
response = httpx.get(current_url, ...) # resolution #2 (connection) -- NOT pinned to #1
Nothing ties the connection to the IP that passed validation. Between the two resolutions a low-TTL attacker-controlled record can flip from a public address (passes the guard) to a private one (used by the connection). The redirect-handling loop in the same function does correctly re-validate each redirect URL, so this is specifically a TOCTOU/rebinding gap in the host-to-IP check, not a redirect issue.
PoC
Self-contained reproducer: https://gist.github.com/thegr1ffyn/c1d54dd6ff2a4c0d7d0dabe00c4985f4
It starts a loopback HTTP server standing in for an internal target and patches socket.getaddrinfo to return a public IP on the guard's lookup and 127.0.0.1 on httpx's the standard deterministic way to demonstrate this TOCTOU class (the real-world trigger is a low-TTL rebinding DNS record the attacker controls).
Reachability in normal use: the attacker registers a rebinding hostname and gets the tool to fetch http://that-host/schema.json either via --url or via a remote $ref in a supplied schema (remote refs are fetched on the default configuration).
Maintainer status
Confirmed by maintainer review and regression tests. The private fix PR was merged and released in 0.63.0: https://github.com/koxudaxi/datamodel-code-generator-ghsa-vx7x-vcc2-c44g/pull/1
Fix summary: pin the validated DNS result set during the HTTP fetch so a host cannot resolve to a safe address during validation and a different address during connection.
Release status: fixed in 0.63.0; 0.62.0 and earlier are affected.
Validation: uv run --group test --extra http pytest tests/test_http.py passed locally for DNS pinning and URL-fetch regression coverage; uv run --group fix ruff check src/datamodel_code_generator/http.py tests/test_http.py passed.
Submitted by: Hamza Haroon (thegr1ffyn)
Impact
Server-side request forgery (CWE-918) via a time-of-check/time-of-use resolution gap (CWE-367). Any service or CI pipeline that runs datamodel-code-generator against attacker-influenced URLs is affected, including deployments that rely on the default private-network protection. Consequences include reading cloud instance-metadata credentials (169.254.169.254), reaching internal-only HTTP services, and port/host probing of the internal network, the document fetched from the internal target is also parsed and can be reflected into the generated output.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-55391 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.63.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-55391? CVE-2026-55391 is a high-severity server-side request forgery (SSRF) vulnerability in datamodel-code-generator (pip), affecting versions <= 0.62.0. It is fixed in 0.63.0. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-55391? CVE-2026-55391 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of datamodel-code-generator are affected by CVE-2026-55391? datamodel-code-generator (pip) versions <= 0.62.0 is affected.
- Is there a fix for CVE-2026-55391? Yes. CVE-2026-55391 is fixed in 0.63.0. Upgrade to this version or later.
- Is CVE-2026-55391 exploitable, and should I be worried? Whether CVE-2026-55391 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-55391 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-55391? Upgrade
datamodel-code-generatorto 0.63.0 or later.