diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cf791e12..2f3bcf0cb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,15 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Security
+
+- **PyYAML Dependency Upgrade** (#9055): Added explicit `pyyaml>=6.0.3` constraint
+  to `pyproject.toml` to proactively pin the dependency to the latest patched release.
+  PyYAML has a history of security vulnerabilities (CVE-2017-18342 and related
+  advisories). The explicit constraint prevents resolution of vulnerable older versions
+  and ensures the lock file always resolves to a safe release. No unsafe `yaml.load()`
+  calls without an explicit `Loader` argument were found in the codebase.
+
 ### Fixed
 
 - **Automation Profile Silent Fallback** (#8232): `_resolve_profile_for_plan` in
diff --git a/pyproject.toml b/pyproject.toml
index 1a0498c9d..e734ff735 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -48,6 +48,7 @@ dependencies = [
     "tomlkit>=0.13.0",  # TOML writing with comment preservation for config CLI
     "tenacity>=8.2.0",  # Retry framework for service layer resilience
     "aiohttp>=3.13.4",  # CVE-2026-34515 mitigation: open redirect vulnerability
+    "pyyaml>=6.0.3",  # Security: explicit pin to latest patched release; prevents resolution of vulnerable older versions
     "a2a-sdk>=0.3.0",  # A2A Python SDK — required transport for local (stdio) and server (HTTP) modes (ADR-047)
 ]