diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7c9d662fd..ed7b4dd9d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -96,6 +96,11 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Security
 
+- **PyYAML upgraded to >=6.0.3 to address known security vulnerability** (#9055):
+  Added an explicit `pyyaml>=6.0.3` dependency constraint to `pyproject.toml` to
+  prevent installation of vulnerable older versions with known YAML parsing security
+  issues.
+
 - **aiohttp upgraded to >=3.13.4 to remediate CVE-2026-34513 and CVE-2026-34515** (#1549, #1544):
   Added an explicit `aiohttp>=3.13.4` dependency constraint to `pyproject.toml` to remediate
   two high-severity open redirect vulnerabilities. Both CVEs affect the CleverAgents platform's
diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index 51815111f..619dd462f 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -33,4 +33,5 @@ Below are some of the specific details of various contributions.
 * HAL 9000 has contributed the LLMTraceRepository data-integrity fix (PR #8185 / issue #7505): replaced the unconditional `session.commit()` in `LLMTraceRepository.save()` with a dual-path implementation that respects the UnitOfWork pattern — flushing only when an external session is provided, and flushing + committing + closing when operating standalone. This eliminates premature transaction commits, loss of rollback capability, and a docstring/implementation mismatch.
 * HAL 9000 has contributed the ACMS Index Data Model and File Traversal Engine (PR #9664 / issue #9579): foundational data structures for indexed context entries with hot/warm/cold/archive storage tier classification, tag system, and a timeout-safe chunked file traversal engine for large projects with 10,000+ files.
 
-* HAL 9000 has contributed the error-suppression removal fix (PR #9247 / issue #9060): removed both `try...except Exception:` blocks in `register_registry_agents()` that silently suppressed errors from `actor_registry.list_actors()` and the route bridge refresh, enabling exceptions to propagate per CONTRIBUTING.md fail-fast policy. Added three Behave scenarios verifying RuntimeError, AttributeError, and TypeError propagation.
\ No newline at end of file
+* HAL 9000 has contributed the error-suppression removal fix (PR #9247 / issue #9060): removed both `try...except Exception:` blocks in `register_registry_agents()` that silently suppressed errors from `actor_registry.list_actors()` and the route bridge refresh, enabling exceptions to propagate per CONTRIBUTING.md fail-fast policy. Added three Behave scenarios verifying RuntimeError, AttributeError, and TypeError propagation.
+ * HAL 9000 has contributed the PyYAML security upgrade (PR #9244 / issue #9055): added `pyyaml>=6.0.3` dependency constraint to address known YAML parsing vulnerabilities.
diff --git a/pyproject.toml b/pyproject.toml
index c1fdf4a71..f711440c7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -47,6 +47,7 @@ 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: address known YAML parsing vulnerabilities
     "a2a-sdk>=0.3.0,<1.0.0",  # A2A Python SDK — required transport for local (stdio) and server (HTTP) modes (ADR-047); pinned <1.0.0 (removed legacy A2AClient)
 ]
 
diff --git a/uv.lock b/uv.lock
index 31d88e524..92b534642 100644
--- a/uv.lock
+++ b/uv.lock
@@ -446,6 +446,7 @@ dependencies = [
     { name = "pydantic" },
     { name = "pydantic-settings" },
     { name = "python-ulid" },
+    { name = "pyyaml" },
     { name = "restrictedpython" },
     { name = "rx" },
     { name = "structlog" },
@@ -529,6 +530,7 @@ requires-dist = [
     { name = "pytest-asyncio", marker = "extra == 'dev'", specifier = ">=0.23.0" },
     { name = "pytest-cov", marker = "extra == 'dev'", specifier = ">=4.1.0" },
     { name = "python-ulid", specifier = ">=2.7.0" },
+    { name = "pyyaml", specifier = ">=6.0.3" },
     { name = "radon", marker = "extra == 'dev'", specifier = ">=6.0.1" },
     { name = "restrictedpython", specifier = ">=7.0" },
     { name = "robotframework", marker = "extra == 'tests'", specifier = ">=7.3.2" },