Security readout for executives and security teams
Plain-English summary
CVE-2021-45939 is a reported heap-based buffer overflow in wolfSSL wolfMQTT 1.9, an MQTT client library. Software that embeds this library may face crash or memory-corruption risk during MQTT packet handling. The sources do not provide CVSS, broader affected inventory, or active exploitation evidence.
Executive priority
Treat this as a targeted dependency-risk item, not a confirmed emergency. Prioritize environments that embed wolfMQTT 1.9 and process MQTT traffic from external or less-trusted networks.
Technical view
The CVE places the flaw in MqttClient_DecodePacket, called from MqttClient_WaitType and MqttClient_Subscribe. It is described as a heap-based buffer overflow in wolfMQTT 1.9 and linked to OSS-Fuzz/OSV records plus a wolfMQTT commit. The bundle does not include exploit details or a named fixed release.
Likely exposure
Exposure is most likely where wolfMQTT 1.9 is embedded in applications, firmware, IoT software, or services that parse MQTT traffic. The provided affected-product data is incomplete.
Exploitation context
The bundle marks KEV as false and provides no cited evidence of active exploitation. OSS-Fuzz linkage suggests the issue was found through fuzz testing, but the sources provided do not establish real-world exploitation.
Researcher notes
Key gaps are missing CVSS, absent CWE metadata, incomplete affected-product fields, and no named fixed release in the bundle. The strongest technical anchors are the function names, wolfMQTT 1.9 version statement, OSS-Fuzz/OSV reference, and linked commit.
Mitigation direction
- Inventory software and firmware for wolfMQTT 1.9 usage.
- Check wolfSSL wolfMQTT guidance and releases for the referenced fix.
- Prioritize updates where MQTT input crosses trust boundaries.
- Apply vendor-supported fixes through normal regression testing.
- If patching is delayed, reduce untrusted MQTT exposure where feasible.
Validation and detection
- Review SBOMs, build manifests, and static links for wolfMQTT 1.9.
- Confirm whether deployed builds include the referenced wolfMQTT commit.
- Verify MQTT-facing components are not using the vulnerable library version.
- Run maintained unit, integration, and fuzz regression tests after updating.
- Document any exceptions where vendor guidance is unavailable.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CVE-2021-45939 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/wolfSSL/wolfMQTT/commit/84d4b53122e0fa0280c7872350b89d5777dabbb2CVE reference · x_refsource_MISC
- https://github.com/google/oss-fuzz-vulns/blob/main/vulns/wolfmqtt/OSV-2021-1361.yamlCVE reference · x_refsource_MISC
- https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=39103CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.