CVE-2025-56353Public exploitNetwork attack vector

Broker crash via retained malformed topic filters

Published Jan 20, 2026 · Updated Jan 20, 2026

Memory leak in tinyMQTT commit 6226ade15bd4f97be2d196352e64dd10937c1962 allows remote attackers to crash the broker via SUBSCRIBE packets. The parse_subscribe_packet routine accepts malformed or oversized UTF-8 topic filters, allocates storage for them, and fails to release that memory. Unauthenticated network access and sustained repeated requests are required; the resulting heap growth interrupts broker availability without reported data disclosure or modification.

CVSS severity7.5
High
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in tinyMQTT commit 6226ade15bd4f97be2d196352e64dd10937c1962 allows remote attackers to crash the broker via SUBSCRIBE packets. The parse_subscribe_packet routine accepts malformed or oversized UTF-8 topic filters, allocates storage for them, and fails to release that memory. Unauthenticated network access and sustained repeated requests are required; the resulting heap growth interrupts broker availability without reported data disclosure or modification.

The record

CVE
CVE-2025-56353
Published
Jan 20, 2026
Updated
Jan 20, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-401, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 20, 2026Record 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 vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.003Application Exhaustion Flood

Public exploit references

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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