CVE-2021-41219: Undefined behavior via `nullptr` reference binding in sparse matrix multiplication

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-11-05 · updated 2026-06-17
Weakness: CWE-824

Description

TensorFlow is an open source platform for machine learning. In affected versions the code for sparse matrix multiplication is vulnerable to undefined behavior via binding a reference to `nullptr`. This occurs whenever the dimensions of `a` or `b` are 0 or less. In the case on one of these is 0, an empty output tensor should be allocated (to conserve the invariant that output tensors are always allocated when the operation is successful) but nothing should be written to it (that is, we should return early from the kernel implementation). Otherwise, attempts to write to this empty tensor would result in heap OOB access. The fix will be included in TensorFlow 2.7.0. We will also cherrypick this commit on TensorFlow 2.6.1, TensorFlow 2.5.2, and TensorFlow 2.4.4, as these are also affected and still in supported range.

Affected products

tensorflow: before 2.4.4; from 2.5.0 before 2.5.2; 2.6.0 — fixed in 2.4.4, 2.5.2

How to fix

Upgrade to a fixed version: tensorflow 2.4.4, 2.5.2. Check the vendor advisory for mitigations.

References

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