VulnerabilityPublished 20 Jan 2026Updated 21 Jan 2026

CVE-2025-56353: tinyMQTT · CVE-2025-56353 is a high-severity

Affects tinyMQTTSource CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 26% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
GitHubjustdoit0910/tinyMQTT`pkg:github/justdoit0910/tinyMQTT`Other threats	Affected *	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Implement strict input validation on MQTT topic filters at the broker level to reject malformed UTF-8 strings before memory allocation.
Deploy network-level rate limiting and anomaly detection to identify and block repeated subscription requests with suspiciously large or invalid payloads.
Isolate MQTT brokers within segmented network zones with limited exposure to untrusted networks to reduce attack surface.
Monitor broker memory usage and system resource metrics continuously to detect abnormal memory growth indicative of exploitation attempts.
Apply any future patches or updates from tinyMQTT maintainers promptly once available.
Consider deploying MQTT gateways or proxies that can sanitize and validate client requests before forwarding them to the broker.
Conduct regular security assessments and penetration tests focusing on MQTT infrastructure to identify and remediate weaknesses.
Educate operational teams about the risks of malformed MQTT messages and establish incident response plans for broker outages.

Description

CVE-2025-56353 is a high-severity vulnerability in tinyMQTT broker software caused by improper handling of malformed UTF-8 strings in topic filters. An attacker can exploit this by sending repeated subscription requests with invalid or oversized topic filters, causing the broker to allocate memory without freeing it, resulting in a memory leak. This unbounded heap growth can lead to denial of service (DoS) conditions under sustained attack. The vulnerability requires no authentication or user interaction and can be exploited remotely over the network. There are no known exploits in the wild yet, and no patches have been published at this time. The CVSS score of 7.5 reflects the high impact on availability with no impact on confidentiality or integrity. European organizations using tinyMQTT brokers in IoT or messaging infrastructures are at risk, especially those with exposed MQTT brokers. Mitigations include implementing input validation and rate limiting at the network perimeter, monitoring broker memory usage, and isolating MQTT services. Countries with significant IoT deployments and industrial automation sectors, such as Germany, France, and the UK, are most likely to be affected.

Impact

For European organizations, the primary impact of CVE-2025-56353 is the risk of denial of service on MQTT broker infrastructure. Many European industries, including manufacturing, energy, transportation, and smart city deployments, rely heavily on MQTT for IoT device communication and telemetry. A successful attack could disrupt critical data flows, causing operational downtime, loss of monitoring capabilities, and potential cascading failures in automated systems. Since the vulnerability does not affect confidentiality or integrity, data breaches or manipulation are unlikely, but service unavailability can have severe operational and financial consequences. Organizations with exposed MQTT brokers or those lacking network segmentation are particularly vulnerable. Additionally, the lack of authentication requirements means attackers can launch attacks from external networks, increasing the threat surface. The absence of known exploits in the wild provides a window for proactive mitigation, but the high severity score indicates that exploitation could have serious consequences if left unaddressed.

CWE-401Missing Release of Memory after Effective Lifetime (opens in a new tab)
Variant weaknessLikelihood of exploit: Medium
The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.
Implementation · Libraries or Frameworks
Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Architecture and Design · Build and Compilation
Consider using the Boehm-Demers-Weiser garbage collector (bdwgc), which can help avoid leaks.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/JustDoIt0910/tinyMQTT/issues/19 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Jan 2026, 20:14 UTC

WeaknessesCWE-401

Technical details

References

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