GitHub Security Advisory: GHSA-36rr-ww3j-vrjv
Package: keras (PIP)
Severity: HIGH (CVSS 0.0)
CWE: CWE-913: Improper Control of Dynamically-Managed Code Resources
Vulnerable versions: >= 3.0.0, < 3.11.3
Patched in: 3.11.3

Summary: The Keras `Model.load_model` method **silently** ignores `safe_mode=True` and allows arbitrary code execution when a `.h5`/`.hdf5` file is loaded.

Details:
**Note:** This report has already been discussed with the Google OSS VRP team, who recommended that I reach out directly to the Keras team. I’ve chosen to do so privately rather than opening a public issue, due to the potential security implications. I also attempted to use the email address listed in your `SECURITY.md`, but received no response.

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## Summary

When a model in the `.h5` (or `.hdf5`) format is loaded using the Keras `Model.load_model` method, the `safe_mode=True` setting is **silently** ignored without any warning or error. This allows an attacker to execute arbitrary code on the victim’s machine with the same privileges as the Keras application. This report is specific to the `.h5`/`.hdf5` file format. The attack works regardless of the other parameters passed to `load_model` and does not require any sophisticated technique—`.h5` and `.hdf5` files are simply not checked for unsafe code execution.

From this point on, I will refer only to the `.h5` file format, though everything equally applies to `.hdf5`.

## Details

### Intended behaviour 
According to the official Keras documentation, `safe_mode` is defined as:

```
safe_mode: Boolean, whether to disallow unsafe lambda deserialization. When safe_mode=False, loading an object has the potential to trigger arbitrary code execution. This argument is only applicable to the Keras v3 model format. Defaults to True.
```
I understand that the behavior described in this report is somehow **intentional**, as `safe_mode` is only applicable to `.keras` models. 

However, in practice, this behavior is misleading for users who are unaware of the internal Keras implementation. `.h5` files can still be loaded seamlessly using `load_model` with `safe_mode=True`, and the absence of any warning or error creates a **false sense of security**. Whether intended or not, I believe silently ignoring a security-related parameter is not the best possible design decision. At a minimum, if `safe_mode` cannot be applied to a given file format, an explicit error should be raised to alert the user.

This issue is particularly critical given the widespread use of the `.h5` format, despite the introduction of newer formats.

As a small anecdotal test, I asked several of my colleagues what they would expect when loading a `.h5` file with `safe_mode=True`. None of them expected the setting to be **silently** ignored, even after reading the documentation. While this is a small sample, all of these colleagues are cybersecurity researchers—experts in binary or ML security—and regular participants in DEF CON finals. I was careful not to give any hints about the vulnerability in our discussion.

### Technical Details

Examining the implementation of `load_model` in `keras/src/saving/saving_api.py`, we can see that the `safe_mode` parameter is completely ignored when loading `.h5` files. Here's the relevant snippet:

```python
def load_model(filepath, custom_objects=None, compile=True, safe_mode=True):
    is_keras_