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CVE Record

CVE-2021-37635: Heap out of bounds access in sparse reduction operations in TensorFlow

TensorFlow is an end-to-end open source platform for machine learning. In affected versions the implementation of sparse reduction operations in TensorFlow can trigger accesses outside of bounds of heap allocated data. The [implementation](https://github.com/tensorflow/tensorflow/blob/a1bc56203f21a5a4995311825ffaba7a670d7747/tensorflow/core/kernels/sparse_reduce_op.cc#L217-L228) fails to validate that each reduction group does not overflow and that each corresponding index does not point to outside the bounds of the input tensor. We have patched the issue in GitHub commit 87158f43f05f2720a374f3e6d22a7aaa3a33f750. 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.

HighCVSS 7.3Not KEV-listedUpdated
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

TensorFlow sparse reduction operations can read or access heap memory outside expected tensor bounds. In ML systems that accept attacker-controlled tensors or model inputs, this could expose data, corrupt results, or crash the process. The issue is high severity but sources do not show known active exploitation.

Executive priority

Prioritize remediation for ML services or pipelines that process untrusted data. The business risk is process crash or data exposure inside TensorFlow workloads, not a broadly remote internet worm scenario based on the provided sources.

Technical view

CVE-2021-37635 affects TensorFlow sparse reduction code that failed to validate reduction group overflow and corresponding index bounds. The advisory maps this to CWE-125 with CVSS 7.3. Patched code was committed and released through TensorFlow 2.6.0 and supported cherrypicks.

Likely exposure

Exposure is most likely where TensorFlow versions before the fixed releases process untrusted or semi-trusted sparse tensor data. Listed affected ranges include TensorFlow 2.5.0 before 2.5.1, 2.4.x before 2.4.3, and versions before 2.3.4.

Exploitation context

The CVSS vector indicates local attack, low complexity, low privileges, and no user interaction. The provided bundle says KEV is false and includes no evidence of active exploitation or public weaponization. Treat exploitation status as not established from these sources.

Researcher notes

Focus review on sparse_reduce_op.cc validation around reduction groups and input tensor index bounds. The source evidence identifies heap out-of-bounds access and CWE-125, but does not provide exploit maturity, bypass notes, or operational indicators.

Mitigation direction

  • Upgrade TensorFlow to 2.6.0 or a later fixed release.
  • For supported older branches, use TensorFlow 2.5.1, 2.4.3, or 2.3.4.
  • Prioritize systems processing untrusted sparse tensor inputs.
  • Check TensorFlow vendor guidance before relying on compensating controls.

Validation and detection

  • Inventory TensorFlow versions in applications, containers, notebooks, and training images.
  • Flag versions matching the affected ranges listed in the advisory.
  • Confirm fixed versions or commit 87158f43f05f2720a374f3e6d22a7aaa3a33f750 are present.
  • Review ML entry points that accept externally supplied sparse tensors.
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

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2021-37635 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.3 (3.1)
Known Exploited
No
Published

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

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
7.3CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H1.85.5Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

7.3High
CVSS 3.1 vector shape for CVE-2021-37635Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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.