VulnerabilityPublished 25 Feb 2026

CVE-2026-27850: Linksys MR9600 · Improper Verification of Source of a Communication Channel

Affects Linksys MR9600Source CVE Database V5

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Not known to be exploited · CVSS 7.5 High.

Data as of 29 Oct 2026, 19:04 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% 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:H/I:N/A:N

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

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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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
LinksysMR9600	Affected =1.0.4.205530	Fixed in–
LinksysMX4200	Affected =1.0.13.210200	Fixed in–

AI-suggested

To mitigate CVE-2026-27850, organizations should immediately review and modify firewall rules on affected Linksys MR9600 and MX4200 routers to block all unsolicited inbound WAN traffic with source port 5222 unless explicitly required and secured. Network administrators should implement strict ingress filtering to prevent unauthorized external access to internal services. If possible, disable or restrict services that listen on port 5222 or related internal services exposed due to this vulnerability. Monitoring network traffic for unusual connection attempts on port 5222 can help detect exploitation attempts. Organizations should prioritize applying official firmware updates or patches from Linksys once released. In the absence of vendor patches, deploying network-level protections such as upstream firewalls or intrusion prevention systems to block suspicious traffic is recommended. Additionally, segmenting critical internal services and enforcing strong authentication and encryption can reduce the impact if exposure occurs. Regular vulnerability scanning and penetration testing should be conducted to verify that the exposure has been mitigated effectively.

Description

Due to an improperly configured firewall rule, the router will accept any connection on the WAN port with the source port 5222, exposing all services which are normally only accessible through the local network. This issue affects MR9600: 1.0.4.205530; MX4200: 1.0.13.210200.

Impact

The primary impact of CVE-2026-27850 is the unauthorized exposure of internal network services to the internet, which can lead to significant confidentiality breaches. Attackers can remotely access services that are normally restricted to trusted local networks, potentially harvesting sensitive information or using these services as pivot points for further internal network compromise. Although the vulnerability does not directly affect data integrity or system availability, the confidentiality loss alone can be severe, especially in enterprise or critical infrastructure environments. The lack of required authentication and user interaction lowers the barrier for exploitation, increasing the risk of automated or opportunistic attacks. Organizations with affected routers face increased risk of data leakage, espionage, or lateral movement by threat actors. This vulnerability could also undermine trust in network security controls and lead to compliance violations if sensitive data is exposed. The absence of known exploits currently provides a window for proactive mitigation, but the risk remains high due to the straightforward nature of the flaw.

CWE-940Improper Verification of Source of a Communication Channel (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product establishes a communication channel to handle an incoming request that has been initiated by an actor, but it does not properly verify that the request is coming from the expected origin.
Architecture and Design
Use a mechanism that can validate the identity of the source, such as a certificate, and validate the integrity of data to ensure that it cannot be modified in transit using an Adversary-in-the-Middle (AITM) attack.
OWASP Cheat Sheets
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V1.14.1 (opens in a new tab)
V14.5.2 (opens in a new tab)
V14.5.3 (opens in a new tab)
Attack patterns
WebView Injection (opens in a new tab)
Connection Reset (opens in a new tab)
TCP RST Injection (opens in a new tab)
Traffic Injection (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2025-014.txt (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Feb 2026, 21:26 UTC

WeaknessesCWE-940

Technical details

References

Community reviews

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