Document disclosed IDOR and GraphQL DoS advisories

Add SECURITY_NOTES.md entries for GHSA-c74x-79w6-63jh (cross-tenant
IDOR via unvalidated Finding->Risk and ProcessingActivity->DPO
references) and GHSA-prh2-g8pv-m7p9 (GraphQL alias-flooding DoS),
ahead of public disclosure.

Signed-off-by: Bryan Frimin <bryan@probo.com>

SECURITY_NOTES.md

@@ -3,6 +3,52 @@
 User-facing notes on security-relevant changes to Probo. For the
 vulnerability reporting process, see [SECURITY.md](SECURITY.md).
 
+## Cross-tenant IDOR via unvalidated foreign-key references
+
+_2026-07-03, GraphQL_
+
+Two console GraphQL resolvers authorized the parent object and then
+resolved a related object with a tenant scope taken from that related
+object's own GID, instead of from the authorization result. An
+authenticated member of one organization could attach another
+organization's Risk or Data Protection Officer profile GID to their own
+Finding or Processing Activity, then read it back:
+
+- `Finding.risk` disclosed another organization's Risk (name,
+  description, treatment, category, severity, owner).
+- `ProcessingActivity.dataProtectionOfficer` disclosed another
+  organization's person profile PII (full name, email addresses,
+  position).
+
+`FindingService` and `ProcessingActivityService` now validate the
+referenced Risk and Data Protection Officer profile against the
+caller's scope before storing the reference, and the affected
+resolvers (along with every other resolver following the same
+pattern) now authorize the related object's own ID rather than the
+parent's.
+
+Reported by [Pig-Tail](https://github.com/Pig-Tail).
+([GHSA-c74x-79w6-63jh](https://github.com/getprobo/probo/security/advisories/GHSA-c74x-79w6-63jh))
+
+## GraphQL alias-flooding denial of service
+
+_2026-06-29, GraphQL_
+
+The GraphQL endpoints (`connect`, `console`, and `trust`) built their
+server with no limits on query size or complexity. A single request
+containing thousands of aliased resolver calls (e.g. `a1: viewer { id
+}` repeated thousands of times) was parsed, executed, and marshalled
+in full, letting an attacker drive excessive CPU and memory use and
+degrade service for other tenants.
+
+The shared GraphQL handler now enforces a parser token limit that
+rejects oversized queries before execution, a fixed query complexity
+limit, and an LRU query cache, with limits configurable per
+environment via `PROBOD_API_GRAPHQL_*` env vars and Helm values.
+
+Reported by [Muthu-Devarajan](https://github.com/Muthu-Devarajan).
+([GHSA-prh2-g8pv-m7p9](https://github.com/getprobo/probo/security/advisories/GHSA-prh2-g8pv-m7p9))
+
 ## Open redirect bypass in saferedirect
 
 _2026-05-26, Auth_