CVE-2025-20271VulnerabilityPublished 18 Jun 2025

CVE-2025-20271: Cisco Meraki MX Firmware · Use of Uninitialized Variable

Affects Cisco Meraki MX FirmwareSource CVE Database V5

Not known to be exploited · CVSS 8.6 High.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

8.6High

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 45% 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:C/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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 18 Jun 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 2026-10-26.

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

Apply Cisco's official firmware updates and patches for Meraki MX and Z Series devices as soon as they become available to address the uninitialized variable issue.

Implement network-level protections such as rate limiting and filtering of HTTPS requests to the VPN server to detect and block suspicious or malformed traffic patterns that could trigger the vulnerability.

Deploy intrusion detection and prevention systems (IDS/IPS) with signatures or heuristics tuned to detect anomalous SSL VPN session establishment attempts.

Segment VPN infrastructure from other critical network segments to contain potential impact and facilitate rapid isolation in case of an attack.

Establish robust monitoring and alerting on VPN server health and session stability to enable rapid detection of service restarts or connection failures.

Prepare incident response playbooks specifically for VPN service disruptions, including communication plans for remote users and fallback access methods.

Consider temporary deployment of alternative remote access solutions or redundant VPN gateways to maintain connectivity during patching or in case of exploitation attempts.

Description

A vulnerability in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the Cisco AnyConnect service on an affected device. This vulnerability is due to variable initialization errors when an SSL VPN session is established. An attacker could exploit this vulnerability by sending a sequence of crafted HTTPS requests to an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to restart, resulting in the failure of all established SSL VPN sessions and forcing remote users to initiate a new VPN connection and re-authenticate. A sustained attack could prevent new SSL VPN connections from being established, effectively making the Cisco AnyConnect VPN service unavailable for all legitimate users.

Impact

For European organizations, this vulnerability poses a significant risk to business continuity and secure remote access operations. Cisco Meraki MX and Z Series devices are widely deployed in enterprise, government, and critical infrastructure networks across Europe to provide secure VPN connectivity for remote workers. A successful DoS attack exploiting this vulnerability could disrupt remote workforce productivity by disconnecting active VPN sessions and preventing new connections, potentially halting access to internal resources and cloud services. This is especially critical for sectors with high remote access dependency such as finance, healthcare, public administration, and technology. Extended downtime could lead to operational delays, increased support costs, and potential regulatory compliance issues related to availability of critical services. Additionally, the disruption could be leveraged as part of a larger attack campaign to distract or delay incident response efforts. Given the unauthenticated nature of the exploit and the lack of user interaction requirements, the threat actor could launch attacks at scale, impacting multiple organizations simultaneously.

References

sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-meraki-mx-vpn-dos-sM5GCfm7 (opens in a new tab)

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 18 Jun 2025, 17:16 UTC

Technical details

References

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