CVE-2021-45937

Client crash via one-byte heap overwrite

Published Dec 31, 2021 · Updated Aug 4, 2024

Heap-based buffer overflow in wolfSSL wolfMQTT 1.9 allows attackers to crash a client process via a crafted MQTT packet. MqttClient_DecodePacket writes one byte beyond a heap buffer while decoding input reached from MqttClient_WaitType and MqttClient_Connect. The client must process attacker-controlled packet data; published evidence establishes an availability impact but does not demonstrate code execution.

CVSS severity5.5
Medium
EPSS probability0.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in wolfSSL wolfMQTT 1.9 allows attackers to crash a client process via a crafted MQTT packet. MqttClient_DecodePacket writes one byte beyond a heap buffer while decoding input reached from MqttClient_WaitType and MqttClient_Connect. The client must process attacker-controlled packet data; published evidence establishes an availability impact but does not demonstrate code execution.

The record

CVE
CVE-2021-45937
Published
Dec 31, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 31, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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