[Security] 9.1.3 release notes (#2652)

Resolves #2609: adds the
9.1.3 Security and Endpoint release notes.

Preview: [Elastic Security >
9.1.3](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/2652/release-notes/elastic-security#elastic-security-9.1.3-release-notes)

---------

Co-authored-by: Benjamin Ironside Goldstein <[email protected]>

Author: natasha-moore-elastic

release-notes/elastic-security/index.md

@@ -27,6 +27,13 @@ To check for security updates, go to [Security announcements for the Elastic sta
 
 % *
 
+## 9.1.3 [elastic-security-9.1.3-release-notes]
+
+### Fixes [elastic-security-9.1.3-fixes]
+* Fixes a bug that prevented the vulnerability findings contextual flyout from showing details [#231778]({{kib-pull}}231778).
+* Fixes an issue preventing the creation of Knowledge Base Index Entries in deployments with a large number of indices/mappings [#231376]({{kib-pull}}231376).
+* Fixes a bug where Linux endpoints would report `process.executable` as a relative, instead of absolute, path.
+
 ## 9.1.2 [elastic-security-9.1.2-release-notes]
 
 ### Features and enhancements [elastic-security-9.1.2-features-enhancements]