CVE-2021-41213: Deadlock in mutually recursive `tf.function` objects

Severity: medium (CVSS 5.5 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: none known
Published: 2021-11-05 · updated 2026-06-17
Weakness: CWE-667

Description

TensorFlow is an open source platform for machine learning. In affected versions the code behind `tf.function` API can be made to deadlock when two `tf.function` decorated Python functions are mutually recursive. This occurs due to using a non-reentrant `Lock` Python object. Loading any model which contains mutually recursive functions is vulnerable. An attacker can cause denial of service by causing users to load such models and calling a recursive `tf.function`, although this is not a frequent scenario. 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: from 2.4.0 before 2.4.4; from 2.5.0 before 2.5.2; from 2.6.0 before 2.6.1; 2.7.0-rc0, 2.7.0-rc1 — fixed in 2.4.4, 2.5.2, 2.6.1

How to fix

Upgrade to a fixed version: tensorflow 2.4.4, 2.5.2, 2.6.1. Check the vendor advisory for mitigations.

References

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