Session operations in eager mode lead to null pointer dereferences

### Impact In eager mode (default in TF 2.0 and later), session operations are invalid. However, users could still call the raw ops associated with them and trigger a null pointer dereference: ```python import tensorflow as tf tf.raw_ops.GetSessionTensor(handle=['\x12\x1a\x07'],dtype=4) ``` ```python import tensorflow as tf tf.raw_ops.DeleteSessionTensor(handle=['\x12\x1a\x07']) ``` The [implementation](https://github.com/tensorflow/tensorflow/blob/eebb96c2830d48597d055d247c0e9aebaea94cd5/tensorflow/core/kernels/session_ops.cc#L104) dereferences the session state pointer without checking if it is valid: ```cc OP_REQUIRES_OK(ctx, ctx->session_state()->GetTensor(name, &val)); ``` Thus, in eager mode, `ctx->session_state()` is nullptr and the call of the member function is undefined behavior. ### Patches We have patched the issue in GitHub commit [ff70c47a396ef1e3cb73c90513da4f5cb71bebba](https://github.com/tensorflow/tensorflow/commit/ff70c47a396ef1e3cb73c90513da4f5cb71bebba). The fix will be included in TensorFlow 2.5.0. We will also cherrypick this commit on TensorFlow 2.4.2, TensorFlow 2.3.3, TensorFlow 2.2.3 and TensorFlow 2.1.4, as these are also affected and still in supported range. ### For more information Please consult [our security guide](https://github.com/tensorflow/tensorflow/blob/master/SECURITY.md) for more information regarding the security model and how to contact us with issues and questions. ### Attribution This vulnerability has been reported by members of the Aivul Team from Qihoo 360.

CVSS 3.1

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L

Severity from

GitHub (reviewed advisory)

Weakness

CWE-476

Also known as

BIT-tensorflow-2021-29518, CVE-2021-29518, PYSEC-2021-155, PYSEC-2021-446, PYSEC-2021-644

• github.com/tensorflow/tensorflow/security/advisories/GHSA-62gx-355r-9fhg
• nvd.nist.gov/vuln/detail/CVE-2021-29518
• github.com/tensorflow/tensorflow/commit/ff70c47a396ef1e3cb73c90513da4f5cb71bebba
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-cpu/PYSEC-2021-446.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow-gpu/PYSEC-2021-644.yaml
• github.com/pypa/advisory-database/tree/main/vulns/tensorflow/PYSEC-2021-155.yaml