VulnerabilityPublished 14 Aug 2025

CVE-2025-51986: Infinite Loop

Source CVE Database V5

Not known to be exploited · CVSS 7.5 High.

Data as of 26 Oct 2026, 09:15 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 14 Aug 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 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

AI-suggested

To mitigate the risk posed by CVE-2025-51986, European organizations should: 1) Immediately identify and inventory all devices and systems using the affected freemodbus demo/LINUXTCP implementation, particularly those running the 2018-09-12 version or similar. 2) Restrict network access to these devices by implementing strict network segmentation and firewall rules to limit exposure to trusted management networks only. 3) Monitor network traffic for anomalous or malformed Modbus TCP packets that could indicate exploitation attempts. 4) Engage with the freemodbus maintainers or vendors to obtain patches or updated versions that address this vulnerability as soon as they become available. 5) Where patching is not immediately possible, consider deploying intrusion prevention systems (IPS) or deep packet inspection (DPI) solutions capable of detecting and blocking malformed packets targeting this vulnerability. 6) Implement robust incident response plans tailored to industrial control system disruptions to minimize operational impact if exploitation occurs. 7) Conduct regular security assessments and penetration testing focused on industrial protocols and devices to identify similar weaknesses.

Description

An issue was discovered in the demo/LINUXTCP implementation of cwalter-at freemodbus v.2018-09-12 allowing attackers to reach an infinite loop via a crafted length value for a packet.

Impact

For European organizations, especially those operating in industrial sectors such as manufacturing, energy, utilities, and critical infrastructure, this vulnerability poses a notable risk. Freemodbus is widely used in embedded systems and industrial automation devices that communicate via Modbus TCP. An attacker exploiting this vulnerability could cause denial of service conditions on affected devices, potentially disrupting industrial processes, halting production lines, or impairing critical infrastructure operations. The infinite loop could lead to device unavailability, impacting operational continuity and safety. Given the increasing digitization and network connectivity of industrial control systems in Europe, this vulnerability could be leveraged in targeted attacks against industrial environments. The lack of authentication requirements means that attackers could exploit the vulnerability remotely if the affected devices are exposed to untrusted networks or insufficiently segmented internal networks. This elevates the risk for European organizations with inadequate network segmentation or exposed industrial control system interfaces.

References

gist.github.com/jyjsunny/a9743a718ed3081b034c11201803f6b4 (opens in a new tab)

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 14 Aug 2025, 18:03 UTC

WeaknessesCWE-835

Technical details

References

Community reviews

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