docs: update changelog entry

Author: boray

CHANGELOG.md

@@ -25,6 +25,12 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   - This is an addition to `ZkProgram.analyzeMethods()` which analyzes all methods of a ZkProgram by executing them.
   - Now only a single method is analyzed at a time.
 
+### Changed
+- `IndexedMerkleMap` has been promoted from the `Experimental` namespace and is now part of the public API. https://github.com/o1-labs/o1js/pull/2114
+- 
+### Fixed
+- The `IndexedMerkleMap` root now includes the tree length in its root(commitment), addressing a vulnerability where a malicious user could insert a larger leaf and render the tree unreconstructable by others.
+  
 ## [2.6.0](https://github.com/o1-labs/o1js/compare/4e23a60...3eef10d) - 2025-05-30
 
 ### Added
@@ -57,11 +63,6 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   repository proof-systems. https://github.com/o1-labs/o1js/pull/2128
 - Added verification key validity checks to `LocalBlockchain`. https://github.com/o1-labs/o1js/pull/2171
 
-### Added
-
-### Changed
-- Export `IndexedMerkleMap` directly from index, instead of Experimental Namespace https://github.com/o1-labs/o1js/pull/2114
-
 ### Fixed
 
 ## [2.4.0](https://github.com/o1-labs/o1js/compare/fb625f...6ff7f8470a) - 2025-04-01