CVE-2026-27953

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

Summary

A Pydantic validation bypass in ormar's model constructor allows any unauthenticated user to skip all field validation — type checks, constraints, @field_validator/@model_validator decorators, choices enforcement, and required-field checks — by injecting "__pk_only__": true into a JSON request body. The unvalidated data is subsequently persisted to the database. This affects the canonical usage pattern recommended in ormar's official documentation and examples.

A secondary __excluded__ parameter injection uses the same design pattern to selectively nullify arbitrary model fields during construction.

Details

Root cause: NewBaseModel.__init__ (ormar/models/newbasemodel.py, line 128) pops __pk_only__ directly from user-supplied **kwargs before any validation occurs:

# ormar/models/newbasemodel.py, lines 128-142
pk_only = kwargs.pop("__pk_only__", False)      # ← extracted from user kwargs
object.__setattr__(self, "__pk_only__", pk_only)

new_kwargs, through_tmp_dict = self._process_kwargs(kwargs)

if not pk_only:
    # Normal path: full Pydantic validation
    new_kwargs = self.serialize_nested_models_json_fields(new_kwargs)
    self.__pydantic_validator__.validate_python(
        new_kwargs, self_instance=self
    )
else:
    # Bypass path: NO validation at all
    fields_set = {self.ormar_config.pkname}
    values = new_kwargs
    object.__setattr__(self, "__dict__", values)       # raw dict written directly
    object.__setattr__(self, "__pydantic_fields_set__", fields_set)

The __pk_only__ flag was designed as an internal optimization for creating lightweight FK placeholder instances in ormar/fields/foreign_key.py (lines 41, 527). However, because it is extracted from **kwargs via .pop() with a False default, any external caller that passes user-controlled data to the model constructor can inject this flag.

Why the canonical FastAPI + ormar pattern is vulnerable:

Ormar's official example (examples/fastapi_quick_start.py, lines 55-58) recommends using ormar models directly as FastAPI request body parameters:

@app.post("/items/", response_model=Item)
async def create_item(item: Item):
    await item.save()
    return item

FastAPI parses the JSON body and calls TypeAdapter.validate_python(body_dict), which triggers ormar's __init__. The __pk_only__ key is popped at line 128 before Pydantic's validator inspects the data, so Pydantic never sees it — even extra='forbid' would not prevent this, because the key is already consumed by ormar.

The ormar Pydantic model_config (set in ormar/models/helpers/pydantic.py, line 108) does not set extra='forbid', providing no protection even in theory.

What is bypassed when __pk_only__=True:

• All type coercion and type checking (e.g., string for int field)
• max_length constraints on String fields
• choices constraints
• All @field_validator and @model_validator decorators
• nullable=False enforcement at the Pydantic level
• Required-field enforcement (only pkname is put in fields_set)
• serialize_nested_models_json_fields() preprocessing

Save path persists unvalidated data to the database:

After construction with pk_only=True, calling .save() (ormar/models/model.py, lines 89-107) reads fields directly from self.__dict__ via _extract_model_db_fields(), then executes table.insert().values(**self_fields) — persisting the unvalidated data to the database with no re-validation.

**Secondary vulnerability — __excluded__…

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

Summary

A Pydantic validation bypass in ormar's model constructor allows any unauthenticated user to skip all field validation — type checks, constraints, @field_validator/@model_validator decorators, choices enforcement, and required-field checks — by injecting "__pk_only__": true into a JSON request body. The unvalidated data is subsequently persisted to the database. This affects the canonical usage pattern recommended in ormar's official documentation and examples.

A secondary __excluded__ parameter injection uses the same design pattern to selectively nullify arbitrary model fields during construction.

Details

Root cause: NewBaseModel.__init__ (ormar/models/newbasemodel.py, line 128) pops __pk_only__ directly from user-supplied **kwargs before any validation occurs:

# ormar/models/newbasemodel.py, lines 128-142
pk_only = kwargs.pop("__pk_only__", False)      # ← extracted from user kwargs
object.__setattr__(self, "__pk_only__", pk_only)

new_kwargs, through_tmp_dict = self._process_kwargs(kwargs)

if not pk_only:
    # Normal path: full Pydantic validation
    new_kwargs = self.serialize_nested_models_json_fields(new_kwargs)
    self.__pydantic_validator__.validate_python(
        new_kwargs, self_instance=self
    )
else:
    # Bypass path: NO validation at all
    fields_set = {self.ormar_config.pkname}
    values = new_kwargs
    object.__setattr__(self, "__dict__", values)       # raw dict written directly
    object.__setattr__(self, "__pydantic_fields_set__", fields_set)

The __pk_only__ flag was designed as an internal optimization for creating lightweight FK placeholder instances in ormar/fields/foreign_key.py (lines 41, 527). However, because it is extracted from **kwargs via .pop() with a False default, any external caller that passes user-controlled data to the model constructor can inject this flag.

Why the canonical FastAPI + ormar pattern is vulnerable:

Ormar's official example (examples/fastapi_quick_start.py, lines 55-58) recommends using ormar models directly as FastAPI request body parameters:

@app.post("/items/", response_model=Item)
async def create_item(item: Item):
    await item.save()
    return item

FastAPI parses the JSON body and calls TypeAdapter.validate_python(body_dict), which triggers ormar's __init__. The __pk_only__ key is popped at line 128 before Pydantic's validator inspects the data, so Pydantic never sees it — even extra='forbid' would not prevent this, because the key is already consumed by ormar.

The ormar Pydantic model_config (set in ormar/models/helpers/pydantic.py, line 108) does not set extra='forbid', providing no protection even in theory.

What is bypassed when __pk_only__=True:

• All type coercion and type checking (e.g., string for int field)
• max_length constraints on String fields
• choices constraints
• All @field_validator and @model_validator decorators
• nullable=False enforcement at the Pydantic level
• Required-field enforcement (only pkname is put in fields_set)
• serialize_nested_models_json_fields() preprocessing

Save path persists unvalidated data to the database:

After construction with pk_only=True, calling .save() (ormar/models/model.py, lines 89-107) reads fields directly from self.__dict__ via _extract_model_db_fields(), then executes table.insert().values(**self_fields) — persisting the unvalidated data to the database with no re-validation.

**Secondary vulnerability — __excluded__…

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "pk_only": true into a JSON request body. By injecting "pk_only": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary excluded parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.