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CVE Record

CVE-2021-37670: Heap OOB in `UpperBound` and `LowerBound` in TensorFlow

TensorFlow is an end-to-end open source platform for machine learning. In affected versions an attacker can read from outside of bounds of heap allocated data by sending specially crafted illegal arguments to `tf.raw_ops.UpperBound`. The [implementation](https://github.com/tensorflow/tensorflow/blob/460e000de3a83278fb00b61a16d161b1964f15f4/tensorflow/core/kernels/searchsorted_op.cc#L85-L104) does not validate the rank of `sorted_input` argument. A similar issue occurs in `tf.raw_ops.LowerBound`. We have patched the issue in GitHub commit 42459e4273c2e47a3232cc16c4f4fff3b3a35c38. The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1, TensorFlow 2.4.3, and TensorFlow 2.3.4, as these are also affected and still in supported range.

MediumCVSS 5.5Not KEV-listedUpdated
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

A user who can run TensorFlow operations locally or through an ML service may cause TensorFlow to read memory beyond expected tensor data. The documented impact is confidentiality, not integrity or availability. This matters most where TensorFlow handles untrusted notebooks, model workloads, or user-controlled tensors.

Executive priority

Treat this as a moderate confidentiality issue. It is not documented as remotely exploitable from the network, but shared ML environments can turn local or low-privilege access into meaningful data exposure risk. Patch during the next security maintenance window, faster for multi-tenant ML systems.

Technical view

CVE-2021-37670 is a heap out-of-bounds read in TensorFlow UpperBound and LowerBound raw ops. The implementation did not validate the rank of sorted_input. Crafted illegal arguments could read outside heap-allocated data. CVSS 3.1 is 5.5, with local access and low privileges required.

Likely exposure

Exposure is likely in systems running affected TensorFlow versions: before 2.3.4, 2.4.0 through before 2.4.3, and 2.5.0 through before 2.5.1. Risk is higher in shared ML platforms or services accepting user-controlled TensorFlow workloads.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation evidence. The described attack requires ability to supply illegal arguments to TensorFlow raw ops, and the CVSS vector indicates local access with low privileges, no user interaction, and confidentiality impact.

Researcher notes

Focus validation on exposure paths where untrusted users can invoke TensorFlow raw operations. The advisory names UpperBound and LowerBound and the missing sorted_input rank validation. Avoid assuming broader TensorFlow API impact beyond the cited operations unless confirmed by vendor sources.

Mitigation direction

  • Upgrade TensorFlow to 2.6.0 or a fixed supported release.
  • Use TensorFlow 2.5.1, 2.4.3, or 2.3.4 where applicable.
  • Review the TensorFlow advisory for vendor-specific guidance.
  • Prioritize shared notebook, training, and inference environments handling untrusted workloads.

Validation and detection

  • Inventory TensorFlow versions in lockfiles, containers, notebooks, and runtime images.
  • Confirm no deployment runs the affected version ranges.
  • Check whether users can submit TensorFlow code or tensors to shared services.
  • Verify dependency scanners flag CVE-2021-37670 where affected versions remain.
Prepared
Confidence
high
Sources
4

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-125: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-37670 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N1.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2021-37670Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone
Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
tensorflowtensorflow>= 2.5.0, < 2.5.1, >= 2.4.0, < 2.4.3, < 2.3.4Listed
Weakness

CWE details

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-125 · source CWE mapping

Out-of-bounds Read

Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.