Remote Code Execution in Splunk Secure Gateway via jsonpickle Deserialization

Repository is a small proof-of-concept package for CVE-2026-20251 affecting Splunk Secure Gateway. It contains one executable Python PoC (poc_cve_2026_20251.py) plus supporting documentation in README.md, hashnode-article.md, and engagement.json. The PoC is not a full end-to-end remote exploit client; instead it demonstrates the two critical exploit primitives that compose the real attack chain: (1) bypass of Splunk Secure Gateway's check_alert_data_valid_json() validator by placing an allowed top-level 'py/object' key first and hiding a malicious sibling 'notification' value containing a py/reduce gadget, and (2) execution of that gadget through jsonpickle.decode(..., safe=True), proving the safe flag does not block py/reduce/function/object restoration paths. The exploit capability described by the repository is authenticated remote code execution on the Splunk host as the Splunk service account, achieved by writing a crafted document into the 'mobile_alerts' KV Store collection via Splunk's REST/API workflow and waiting for Secure Gateway to deserialize it. The included payload is intentionally benign: subprocess.check_output(['uname','-a']) to print system information. Fingerprintable targets and context include the local test host 127.0.0.1, Splunk management port 8089, KV Store/mongod port 8191, the SSG bundled library path /Applications/Splunk/etc/apps/splunk_secure_gateway/lib, and vulnerable source files under bin/spacebridgeapp/. Overall, this is a credible, non-weaponized Python POC focused on vulnerability verification and exploit-chain explanation rather than automated exploitation.