4 Unpatched Bugs Plague Grandstream ATAs for VoIP Users

Multiple high-severity vulnerabilities in the Grandstream HT800 series of Analog Telephone Adaptors (ATAs) threaten home office and midrange users alike, with outages, eavesdropping and device takeover.

The HT800 series of ATAs is designed for everyone from home or small-office users to medium-sized businesses, looking to connect their analog telephone devices to a VoIP network, unified communications system or other IP-based communications infrastructure. According to analysis from Tenable, the models have four worrying flaws, all of them unpatched as of this writing.

The bug tracked as CVE-2020-5760 (rating 7.8 out of 10 on the CvSS scale) could allow command injection during the provisioning process. Unauthenticated remote attackers can execute arbitrary commands as root by crafting a special configuration file and sending a crafted SIP message.

“Tenable found the HT800 series is vulnerable to command injection via the configuration file when P240 is set to 1 and P2 (password) contains shell metacharacters,” the firm said in its advisory, released this week. “Furthermore, Tenable found that an unauthenticated remote attacker could trigger this injection via a x-gs-ucm-url SIP message.”

Tenable also published a proof-of-concept exploit, which results in a root shell on the device, allowing full compromise.

Meanwhile, CVE-2020-5761 is an infinite loop problem in the TR-069 service (rated 7.5 out of 10 on the CvSS scale) that can result in CPU exhaustion. The TR-069 is a technical specification of the Broadband Forum that defines an application layer protocol for remote management of customer-premises equipment (CPE) connected to IP networks. In Grandstream’s ATA implementation of it, a bug could allow an unauthenticated remote attacker to trigger an exploit by sending a one-character TCP message to the service.

“The device’s TR-069 service falls into an infinite loop if an unauthenticated, remote attackers sends a TCP message that doesn’t contain a carriage return character (‘\r’),” explained Tenable, in its advisory. “The TR-069 service will then consume almost all of the system’s CPU until the system is rebooted.”

The bug is “trivial” to trigger, the firm added.

The TR-069 service is also at the heart of the third issue, CVE-2020-5762 (rating 7.5 out of 10 on the CvSS scale). This is a denial-of-service issue caused by a NULL pointer dereference in the TR-069 service. The condition is triggered due to mishandling of the HTTP Authentication field, according to the CVE description.

“The device’s TR-069 service will crash due to a NULL pointer dereference when an unauthenticated remote HTTP GET request contains an authentication field that isn’t a well-formed digest-challenge,” according to Tenable. “The TR-069 service doesn’t get restarted after the crash…This is easily reproduced by using basic authentication with curl.”

And finally, CVE-2020-5763 (ranking 8.8 out of 10 on the CvSS scale) is a SSH backdoor allowing a root shell, first uncovered by Lorenzo Santina (BigNerd95) back in January. ” An authenticated remote attacker can obtain a root shell by correctly answering a challenge prompt,” according to the SVE description.

All for now remain unaddressed. Grandstream HT800 series current firmware version 1.0.17.5 and below is vulnerable to all four bugs.

“At the time of publication, no solution exists,” Tenable noted.

Threatpost has reached out to Grandstream about the timeline for issuing a fix for the issues. But in the disclosure timeline, it’s noted that fixes for all the bugs have at least been developed and tested with positive results both by Grandstream internally and by Tenable, as of June 22.

Grandstream has run into other cybersecurity trouble in the past; last year, a series of both unauthenticated and authenticated remote code-execution vulnerabilities were uncovered in a variety of Grandstream products for small to medium-sized businesses, including audio and video conferencing units, IP video phones, routers and IP PBXs.

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