Mitel SIP Phone Flaws Allow Attackers to Inject Malicious Commands

A pair of vulnerabilities in Mitel’s 6800 Series, 6900 Series, and 6900w Series SIP Phones-including the 6970 Conference Unit-could enable attackers to execute arbitrary commands or upload malicious files to compromised devices, posing significant risks to enterprise communication systems.

The flaws, disclosed in Mitel’s Product Security Advisory MISA-2025-0004, include a critical-severity command injection bug (CVE-2025-47188) and a medium-severity unauthenticated file upload vulnerability (CVE-2025-47187).

These issues affect devices running firmware versions R6.4.0.SP4 and earlier, with Mitel urging immediate upgrades to R6.4.0.SP5 or newer releases to mitigate exploitation risks.

Critical Command Injection Vulnerability

The command injection vulnerability (CVE-2025-47188) stems from insufficient sanitization of user-supplied input in the phones’ software, allowing unauthenticated attackers to execute arbitrary operating system commands remotely.

With a CVSS v3.1 score of 9.8, this flaw enables threat actors to manipulate device functionality, access sensitive configuration data, or disrupt operations entirely.

Exploitation requires network access to the affected device, but Mitel’s engineering guidelines emphasize that these phones are typically deployed on internal networks, which may reduce-but not eliminate-exposure to external attacks.

Successful exploitation could lead to unauthorized configuration changes, interception of call data, or permanent device compromise if attackers establish persistence.

Mitel’s advisory notes that the vulnerability impacts all four product lines equally, with no differences in exploit complexity across models.

The lack of authentication requirements heightens the risk, as attackers do not need valid credentials to trigger the flaw.

Security researchers warn that unpatched devices in poorly segmented networks could serve as entry points for lateral movement, particularly in environments where SIP phones share network segments with critical infrastructure.

Unauthenticated File Upload

The secondary vulnerability (CVE-2025-47187), rated 5.3 on the CVSS scale, allows unauthenticated attackers to upload arbitrary WAV files to the devices’ storage systems.

While this flaw does not directly enable code execution or data theft, it could be weaponized to exhaust available storage space-potentially disrupting voice messaging features or causing intermittent service degradation.

Mitel classifies this as a medium-risk issue due to its limited impact on device availability, though prolonged attacks might necessitate manual intervention to purge malicious files.

Notably, both vulnerabilities share a common root cause in inadequate authentication mechanisms.

The file upload flaw specifically bypasses checks that should restrict audio file modifications to authorized users, creating opportunities for low-effort denial-of-service attacks.

While less severe than the command injection issue, this vulnerability underscores broader concerns about input validation and privilege management in Mitel’s firmware architecture.

Mitel has released firmware version R6.4.0.SP5 to address both vulnerabilities, recommending that all organizations using affected devices prioritize updates.

For enterprises unable to immediately deploy patches, Mitel suggests restricting network access to SIP phones through firewall rules and segmenting voice communication systems from general corporate networks.

The company’s Knowledge Base article (SO8496) provides additional mitigation guidance, though details remain restricted to authenticated users and partners.

The vulnerabilities were jointly reported by Marc Bollhalder of InfoGuard Labs, highlighting the ongoing role of independent security researchers in identifying enterprise system weaknesses.

Mitel has not disclosed whether these flaws were exploited in the wild prior to patching, but the critical nature of CVE-2025-47188 suggests organizations should treat remediation as urgent.

Enterprises using Mitel’s Open SIP platform are advised to contact [email protected] for tailored assistance, while other customers should coordinate updates through Mitel Authorized Partners.

These vulnerabilities underscore the evolving threats facing VoIP and unified communication systems, which increasingly serve as attack vectors due to their network accessibility and integration with critical business processes.

The command injection flaw, in particular, reflects systemic risks associated with legacy firmware architectures that lack modern input validation safeguards.

Organizations using Mitel’s affected devices should conduct thorough network audits to identify unprotected endpoints and monitor for anomalous traffic patterns indicative of exploitation attempts.

While Mitel’s recommended network segmentation strategies may reduce attack surfaces, the long-term solution lies in adopting a proactive firmware update regimen.

Security teams are encouraged to automate patch management processes for SIP devices and integrate voice infrastructure into broader vulnerability scanning protocols.

As VoIP systems continue to converge with IT networks, the discovery of CVE-2025-47188 and CVE-2025-47187 serves as a reminder that even specialized hardware requires rigorous security maintenance to prevent compromise.

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