diff --git a/tests/test_config.py b/tests/test_config.py
index c0bd4b14ff8d..d63812d4fc05 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1487,3 +1487,275 @@ def test_ir_op_priority_ctx():
         # context restored even after exception
         assert ir.ops.rms_norm.get_priority() == ["vllm_c", "native"]
         assert ir.ops.fused_add_rms_norm.get_priority() == ["native"]
+
+
+# Config validation tests for field validators added to prevent invalid values
+
+
+@pytest.mark.parametrize("bad", [-1, -5, -100, 0])
+def test_attention_flash_attn_max_num_splits_rejects_non_positive(bad):
+    """flash_attn_max_num_splits_for_cuda_graph must be positive (> 0).
+    Negative or zero values would cause issues in CUDA graph setup."""
+    from vllm.config.attention import AttentionConfig
+
+    with pytest.raises(ValidationError, match="flash_attn_max_num_splits"):
+        AttentionConfig(flash_attn_max_num_splits_for_cuda_graph=bad)
+
+
+@pytest.mark.parametrize("good", [1, 16, 32, 64])
+def test_attention_flash_attn_max_num_splits_accepts_positive(good):
+    from vllm.config.attention import AttentionConfig
+
+    cfg = AttentionConfig(flash_attn_max_num_splits_for_cuda_graph=good)
+    assert cfg.flash_attn_max_num_splits_for_cuda_graph == good
+
+
+@pytest.mark.parametrize("bad", [-1, -5, 0])
+def test_attention_tq_max_kv_splits_rejects_non_positive(bad):
+    """tq_max_kv_splits_for_cuda_graph must be positive (> 0)."""
+    from vllm.config.attention import AttentionConfig
+
+    with pytest.raises(ValidationError, match="tq_max_kv_splits"):
+        AttentionConfig(tq_max_kv_splits_for_cuda_graph=bad)
+
+
+@pytest.mark.parametrize("good", [1, 16, 32, 64])
+def test_attention_tq_max_kv_splits_accepts_positive(good):
+    from vllm.config.attention import AttentionConfig
+
+    cfg = AttentionConfig(tq_max_kv_splits_for_cuda_graph=good)
+    assert cfg.tq_max_kv_splits_for_cuda_graph == good
+
+
+@pytest.mark.parametrize("bad", [0, 8, 15, 17, 31, 33])
+def test_attention_flex_attn_block_size_rejects_invalid(bad):
+    """flex_attn_block_m/n must be >= 16 and power of 2."""
+    from vllm.config.attention import AttentionConfig
+
+    with pytest.raises(ValidationError, match="flex_attn"):
+        AttentionConfig(flex_attn_block_m=bad)
+    with pytest.raises(ValidationError, match="flex_attn"):
+        AttentionConfig(flex_attn_block_n=bad)
+
+
+@pytest.mark.parametrize("good", [16, 32, 64, 128, 256])
+def test_attention_flex_attn_block_size_accepts_valid(good):
+    from vllm.config.attention import AttentionConfig
+
+    cfg = AttentionConfig(flex_attn_block_m=good, flex_attn_block_n=good)
+    assert cfg.flex_attn_block_m == good
+    assert cfg.flex_attn_block_n == good
+
+
+@pytest.mark.parametrize("bad", [0, 3, 7, 15, 17, 31, 33])
+def test_attention_flex_attn_logical_block_size_rejects_non_power_of_2(bad):
+    """flex_attn_q_block_size/kv_block_size must be power of 2."""
+    from vllm.config.attention import AttentionConfig
+
+    with pytest.raises(ValidationError, match="power of 2"):
+        AttentionConfig(flex_attn_q_block_size=bad)
+    with pytest.raises(ValidationError, match="power of 2"):
+        AttentionConfig(flex_attn_kv_block_size=bad)
+
+
+@pytest.mark.parametrize("good", [1, 2, 4, 8, 16, 32, 64, 128])
+def test_attention_flex_attn_logical_block_size_accepts_power_of_2(good):
+    from vllm.config.attention import AttentionConfig
+
+    cfg = AttentionConfig(flex_attn_q_block_size=good, flex_attn_kv_block_size=good)
+    assert cfg.flex_attn_q_block_size == good
+    assert cfg.flex_attn_kv_block_size == good
+
+
+@pytest.mark.parametrize("bad", [-1, -100, 0])
+def test_kv_events_buffer_steps_rejects_non_positive(bad):
+    """buffer_steps must be positive (> 0)."""
+    from vllm.config.kv_events import KVEventsConfig
+
+    with pytest.raises(ValidationError, match="buffer_steps"):
+        KVEventsConfig(buffer_steps=bad)
+
+
+@pytest.mark.parametrize("good", [1, 100, 10_000, 100_000])
+def test_kv_events_buffer_steps_accepts_positive(good):
+    from vllm.config.kv_events import KVEventsConfig
+
+    cfg = KVEventsConfig(buffer_steps=good)
+    assert cfg.buffer_steps == good
+
+
+@pytest.mark.parametrize("bad", [-1, -100, 0])
+def test_kv_events_hwm_rejects_non_positive(bad):
+    """hwm (high water mark) must be positive (> 0)."""
+    from vllm.config.kv_events import KVEventsConfig
+
+    with pytest.raises(ValidationError, match="hwm"):
+        KVEventsConfig(hwm=bad)
+
+
+@pytest.mark.parametrize("good", [1, 1000, 100_000])
+def test_kv_events_hwm_accepts_positive(good):
+    from vllm.config.kv_events import KVEventsConfig
+
+    cfg = KVEventsConfig(hwm=good)
+    assert cfg.hwm == good
+
+
+@pytest.mark.parametrize("bad", [-1, 0])
+def test_kv_events_max_queue_size_rejects_non_positive(bad):
+    """max_queue_size must be positive (> 0)."""
+    from vllm.config.kv_events import KVEventsConfig
+
+    with pytest.raises(ValidationError, match="max_queue_size"):
+        KVEventsConfig(max_queue_size=bad)
+
+
+@pytest.mark.parametrize("good", [1, 1000, 100_000])
+def test_kv_events_max_queue_size_accepts_positive(good):
+    from vllm.config.kv_events import KVEventsConfig
+
+    cfg = KVEventsConfig(max_queue_size=good)
+    assert cfg.max_queue_size == good
+
+
+@pytest.mark.parametrize("bad", [-1.0, -100.0, 0.0, -0.1])
+def test_kv_transfer_buffer_size_rejects_non_positive(bad):
+    """kv_buffer_size must be positive (> 0)."""
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    with pytest.raises(ValidationError, match="kv_buffer_size"):
+        KVTransferConfig(kv_buffer_size=bad)
+
+
+@pytest.mark.parametrize("good", [1.0, 1e9, 1e10])
+def test_kv_transfer_buffer_size_accepts_positive(good):
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    cfg = KVTransferConfig(kv_buffer_size=good)
+    assert cfg.kv_buffer_size == good
+
+
+@pytest.mark.parametrize("bad", [-1, -5, -100])
+def test_kv_transfer_rank_rejects_negative(bad):
+    """kv_rank must be non-negative (>= 0) when set."""
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    with pytest.raises(ValidationError, match="kv_rank"):
+        KVTransferConfig(kv_rank=bad)
+
+
+@pytest.mark.parametrize("good", [0, 1, 2, 10])
+def test_kv_transfer_rank_accepts_non_negative(good):
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    cfg = KVTransferConfig(kv_rank=good)
+    assert cfg.kv_rank == good
+
+
+def test_kv_transfer_rank_accepts_none():
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    cfg = KVTransferConfig(kv_rank=None)
+    assert cfg.kv_rank is None
+
+
+@pytest.mark.parametrize("bad", [-1, 0])
+def test_kv_transfer_parallel_size_rejects_non_positive(bad):
+    """kv_parallel_size must be positive (> 0)."""
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    with pytest.raises(ValidationError, match="kv_parallel_size"):
+        KVTransferConfig(kv_parallel_size=bad)
+
+
+@pytest.mark.parametrize("good", [1, 2, 4, 8])
+def test_kv_transfer_parallel_size_accepts_positive(good):
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    cfg = KVTransferConfig(kv_parallel_size=good)
+    assert cfg.kv_parallel_size == good
+
+
+@pytest.mark.parametrize("bad", [-1, 0, 65536, 100000])
+def test_kv_transfer_port_rejects_invalid_range(bad):
+    """kv_port must be in valid port range [1, 65535]."""
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    with pytest.raises(ValidationError, match="port"):
+        KVTransferConfig(kv_port=bad)
+
+
+@pytest.mark.parametrize("good", [1, 80, 443, 8080, 14579, 65535])
+def test_kv_transfer_port_accepts_valid_range(good):
+    from vllm.config.kv_transfer import KVTransferConfig
+
+    cfg = KVTransferConfig(kv_port=good)
+    assert cfg.kv_port == good
+
+
+@pytest.mark.parametrize("bad", [-1.0, 0.0, -100.0])
+def test_ec_transfer_buffer_size_rejects_non_positive(bad):
+    """ec_buffer_size must be positive (> 0)."""
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    with pytest.raises(ValidationError, match="ec_buffer_size"):
+        ECTransferConfig(ec_buffer_size=bad)
+
+
+@pytest.mark.parametrize("good", [1.0, 1e9, 1e10])
+def test_ec_transfer_buffer_size_accepts_positive(good):
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    cfg = ECTransferConfig(ec_buffer_size=good)
+    assert cfg.ec_buffer_size == good
+
+
+@pytest.mark.parametrize("bad", [-1, -5])
+def test_ec_transfer_rank_rejects_negative(bad):
+    """ec_rank must be non-negative (>= 0) when set."""
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    with pytest.raises(ValidationError, match="ec_rank"):
+        ECTransferConfig(ec_rank=bad)
+
+
+@pytest.mark.parametrize("good", [0, 1, 2])
+def test_ec_transfer_rank_accepts_non_negative(good):
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    cfg = ECTransferConfig(ec_rank=good)
+    assert cfg.ec_rank == good
+
+
+@pytest.mark.parametrize("bad", [-1, 0])
+def test_ec_transfer_parallel_size_rejects_non_positive(bad):
+    """ec_parallel_size must be positive (> 0)."""
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    with pytest.raises(ValidationError, match="ec_parallel_size"):
+        ECTransferConfig(ec_parallel_size=bad)
+
+
+@pytest.mark.parametrize("good", [1, 2, 4])
+def test_ec_transfer_parallel_size_accepts_positive(good):
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    cfg = ECTransferConfig(ec_parallel_size=good)
+    assert cfg.ec_parallel_size == good
+
+
+@pytest.mark.parametrize("bad", [-1, 0, 65536, 100000])
+def test_ec_transfer_port_rejects_invalid_range(bad):
+    """ec_port must be in valid port range [1, 65535]."""
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    with pytest.raises(ValidationError, match="port"):
+        ECTransferConfig(ec_port=bad)
+
+
+@pytest.mark.parametrize("good", [1, 80, 14579, 65535])
+def test_ec_transfer_port_accepts_valid_range(good):
+    from vllm.config.ec_transfer import ECTransferConfig
+
+    cfg = ECTransferConfig(ec_port=good)
+    assert cfg.ec_port == good
diff --git a/vllm/config/attention.py b/vllm/config/attention.py
index 52ce9f102a6c..15bf19bf6caa 100644
--- a/vllm/config/attention.py
+++ b/vllm/config/attention.py
@@ -109,3 +109,42 @@ def validate_mla_prefill_backend_before(cls, value: Any) -> Any:
         if isinstance(value, str):
             return MLAPrefillBackendEnum[value.upper()]
         return value
+
+    @field_validator("flash_attn_max_num_splits_for_cuda_graph", mode="after")
+    @classmethod
+    def _check_flash_attn_max_num_splits(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(
+                f"flash_attn_max_num_splits_for_cuda_graph must be "
+                f"positive (> 0), got {v}."
+            )
+        return v
+
+    @field_validator("tq_max_kv_splits_for_cuda_graph", mode="after")
+    @classmethod
+    def _check_tq_max_kv_splits(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(
+                f"tq_max_kv_splits_for_cuda_graph must be positive (> 0), got {v}."
+            )
+        return v
+
+    @field_validator("flex_attn_block_m", "flex_attn_block_n", mode="after")
+    @classmethod
+    def _check_flex_attn_block_size(cls, v: int | None) -> int | None:
+        if v is not None:
+            if v < 16:
+                raise ValueError(f"flex_attn block size must be >= 16, got {v}.")
+            # Check if power of 2
+            if v & (v - 1) != 0:
+                raise ValueError(f"flex_attn block size must be a power of 2, got {v}.")
+        return v
+
+    @field_validator("flex_attn_q_block_size", "flex_attn_kv_block_size", mode="after")
+    @classmethod
+    def _check_flex_attn_logical_block_size(cls, v: int | None) -> int | None:
+        if v is not None and v & (v - 1) != 0:
+            raise ValueError(
+                f"flex_attn logical block size must be a power of 2, got {v}."
+            )
+        return v
diff --git a/vllm/config/ec_transfer.py b/vllm/config/ec_transfer.py
index a3a927d51ec4..6aec5bae1f46 100644
--- a/vllm/config/ec_transfer.py
+++ b/vllm/config/ec_transfer.py
@@ -5,6 +5,8 @@
 from dataclasses import field
 from typing import Any, Literal, get_args
 
+from pydantic import field_validator
+
 from vllm.config.utils import config
 
 ECProducer = Literal["ec_producer", "ec_both"]
@@ -75,6 +77,36 @@ def compute_hash(self) -> str:
         hash_str = hashlib.md5(str(factors).encode(), usedforsecurity=False).hexdigest()
         return hash_str
 
+    @field_validator("ec_buffer_size", mode="after")
+    @classmethod
+    def _check_ec_buffer_size(cls, v: float) -> float:
+        if v <= 0:
+            raise ValueError(f"ec_buffer_size must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("ec_rank", mode="after")
+    @classmethod
+    def _check_ec_rank(cls, v: int | None) -> int | None:
+        if v is not None and v < 0:
+            raise ValueError(f"ec_rank must be non-negative (>= 0) when set, got {v}.")
+        return v
+
+    @field_validator("ec_parallel_size", mode="after")
+    @classmethod
+    def _check_ec_parallel_size(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(f"ec_parallel_size must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("ec_port", mode="after")
+    @classmethod
+    def _check_ec_port(cls, v: int) -> int:
+        if not (1 <= v <= 65535):
+            raise ValueError(
+                f"ec_port must be in valid port range [1, 65535], got {v}."
+            )
+        return v
+
     def __post_init__(self) -> None:
         if self.engine_id is None:
             self.engine_id = str(uuid.uuid4())
diff --git a/vllm/config/kv_events.py b/vllm/config/kv_events.py
index d618bc9a73f3..cefbc271b09d 100644
--- a/vllm/config/kv_events.py
+++ b/vllm/config/kv_events.py
@@ -4,6 +4,8 @@
 
 from typing import Literal
 
+from pydantic import field_validator
+
 from vllm.config.utils import config
 
 
@@ -47,6 +49,27 @@ class KVEventsConfig:
     this topic to receive events.
     """
 
+    @field_validator("buffer_steps", mode="after")
+    @classmethod
+    def _check_buffer_steps(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(f"buffer_steps must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("hwm", mode="after")
+    @classmethod
+    def _check_hwm(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(f"hwm (high water mark) must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("max_queue_size", mode="after")
+    @classmethod
+    def _check_max_queue_size(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(f"max_queue_size must be positive (> 0), got {v}.")
+        return v
+
     def __post_init__(self):
         if self.publisher is None:
             self.publisher = "zmq" if self.enable_kv_cache_events else "null"
diff --git a/vllm/config/kv_transfer.py b/vllm/config/kv_transfer.py
index b22af99f703f..0b93f3da9e7f 100644
--- a/vllm/config/kv_transfer.py
+++ b/vllm/config/kv_transfer.py
@@ -5,6 +5,8 @@
 from dataclasses import field
 from typing import Any, Literal, get_args
 
+from pydantic import field_validator
+
 from vllm.config.utils import config
 from vllm.utils.hashing import safe_hash
 
@@ -90,6 +92,36 @@ def compute_hash(self) -> str:
         hash_str = safe_hash(str(factors).encode(), usedforsecurity=False).hexdigest()
         return hash_str
 
+    @field_validator("kv_buffer_size", mode="after")
+    @classmethod
+    def _check_kv_buffer_size(cls, v: float) -> float:
+        if v <= 0:
+            raise ValueError(f"kv_buffer_size must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("kv_rank", mode="after")
+    @classmethod
+    def _check_kv_rank(cls, v: int | None) -> int | None:
+        if v is not None and v < 0:
+            raise ValueError(f"kv_rank must be non-negative (>= 0) when set, got {v}.")
+        return v
+
+    @field_validator("kv_parallel_size", mode="after")
+    @classmethod
+    def _check_kv_parallel_size(cls, v: int) -> int:
+        if v <= 0:
+            raise ValueError(f"kv_parallel_size must be positive (> 0), got {v}.")
+        return v
+
+    @field_validator("kv_port", mode="after")
+    @classmethod
+    def _check_kv_port(cls, v: int) -> int:
+        if not (1 <= v <= 65535):
+            raise ValueError(
+                f"kv_port must be in valid port range [1, 65535], got {v}."
+            )
+        return v
+
     def __post_init__(self) -> None:
         if self.engine_id is None:
             self.engine_id = str(uuid.uuid4())