VulnerabilityPublished 2 Dec 2025

CVE-2025-10543: Eclipse Foundation paho.mqtt.golang (Go MQTT v3.1 library) · Incorrect Conversion Between Numeric Types

Affects Eclipse Foundation paho.mqtt.golang (Go MQTT v3.1 library)Source CVE Database V5

Not known to be exploited · CVSS 6.3 Medium.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 4.0 base score

6.3Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 13% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Dec 2025
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
Eclipse Foundation paho.mqtt.golang (Go MQTT v3.1 library)	Affected =0 <=1.5.0	Fixed in–

AI-suggested

Immediately audit all systems and applications using the paho.mqtt.golang library to identify versions <=1.5.0.
Apply patches or updates from the Eclipse Foundation as soon as they become available to fix the numeric conversion issue.
Implement strict input validation on MQTT message lengths at the application layer to reject or truncate UTF-8 strings exceeding 65535 bytes before passing them to the library.
Deploy network-level MQTT protocol anomaly detection and filtering to identify and block malformed packets that could exploit this vulnerability.
Use MQTT brokers and clients that enforce maximum topic and payload sizes consistent with protocol specifications to prevent oversized messages.
Monitor MQTT traffic logs for unusual patterns or errors indicating malformed packets or data leakage.
For critical environments, consider isolating MQTT communication networks and applying strict access controls to limit exposure.
Engage with vendors and open-source communities to track vulnerability disclosures and remediation status.
Conduct security testing and fuzzing of MQTT implementations to detect similar numeric conversion or truncation issues proactively.

Description

In Eclipse Paho Go MQTT v3.1 library (paho.mqtt.golang) versions <=1.5.0 UTF-8 encoded strings, passed into the library, may be incorrectly encoded if their length exceeds 65535 bytes. This may lead to unexpected content in packets sent to the server (for example, part of an MQTT topic may leak into the message body in a PUBLISH packet). The issue arises because the length of the data passed in was converted from an int64/int32 (depending upon CPU) to an int16 without checks for overflows. The int16 length was then written, followed by the data (e.g.topic). This meant that when the data (e.g.topic) was over 65535 bytes then the amount of data written exceeds what the length field indicates. This could lead to a corrupt packet, or mean that the excess data leaks into another field (e.g.topic leaks into message body).

Impact

For European organizations, the impact of CVE-2025-10543 can be significant in sectors relying heavily on MQTT for IoT device communication, industrial automation, smart city infrastructure, and real-time telemetry. The vulnerability can lead to leakage of sensitive topic information into message payloads, potentially exposing confidential data or operational details. Packet corruption may disrupt message delivery, causing loss of data integrity and availability of critical services. This can affect manufacturing plants, energy grids, transportation systems, and healthcare devices that use MQTT for messaging. The medium severity rating indicates moderate risk, but the widespread use of MQTT in IoT ecosystems across Europe elevates the importance of addressing this flaw. Attackers could exploit this vulnerability remotely without authentication, increasing the attack surface. The lack of known exploits currently reduces immediate risk but does not eliminate the potential for future exploitation. Organizations may face operational disruptions, data confidentiality breaches, and compliance risks if unmitigated.

CWE-681Incorrect Conversion between Numeric Types (opens in a new tab)
Base weaknessLikelihood of exploit: High
When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.
Implementation
Avoid making conversion between numeric types. Always check for the allowed ranges.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-197Numeric Truncation Error (opens in a new tab)
Base weaknessLikelihood of exploit: Low
Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.
Implementation
Ensure that no casts, implicit or explicit, take place that move from a larger size primitive or a smaller size primitive.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

gitlab.eclipse.org/security/vulnerability-reports/-/issues/254 (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 2 Dec 2025, 14:13 UTC

WeaknessesCWE-681, CWE-197

Technical details

References

Community reviews

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