Microsoft today took the unusual step of issuing security fixes for out-of-support systems to patch a vulnerability it fears could be wormable if exploited. CVE-2019-0708 affects in-support systems Windows 7, Server 2008, and 2008 R2 and out-of-support Windows 2003 and XP.
It's a critical remote code execution flaw in Remote Desktop Services (RDS), formerly known as Terminal Services, which affects some older versions of Windows. CVE-2019-0708 is pre-authentication and requires no user interaction, meaning any future malware could propagate across vulnerable machines.
Authenticated attackers could exploit this vulnerability by connecting to a target system via Remote Desktop Protocol (RDP) and sending specially crafted requests. Microsoft says RDP itself is not vulnerable; however, it is a component of an attack chain exploiting RDS. If successful, an attacker could execute code on the target system; install programs; view, edit, or delete data; or create new accounts with full user rights. Today's fix corrects the way Remote Desktop Services handles connection requests.
Simon Pope, director of incident response for the Microsoft Security Response Center, says it's "highly likely" malicious actors will write an exploit for this vulnerability and build it into malware. Microsoft has not seen any evidence of CVE-2019-0708 being exploited in the wild, but it urges companies to update immediately, warning the bug could be weaponized as a worm.
The impact is limited to older versions of Windows that are either out of support or approaching the end-of-support life cycle. Vulnerable in-support systems with automatic updates enabled are protected. Vulnerable out-of-support versions can find guidance here.
There is a partial mitigation on affected systems with Network Level Authentication (NLA) enabled, Pope explains in a blog post. These systems are protected from wormable malware or advanced threats that could exploit this vulnerability; NLA requires authentication before the vuln can be triggered. These systems are exposed to RCE if an attacker has valid credentials.
It's worth noting CVE-2019-0708 does not affect newer versions of Windows, including Windows 10, 8.1, and 8, as well as Windows Server 2019, Server 2016, Server 2012 R2, and Server 2012.
CVE-2019-0708 isn't the only vulnerability Microsoft fixed for this month's Patch Tuesday update. The company issued patches for 79 CVEs, 22 of which were deemed Critical in severity and 57 of which were ranked Important. Two were publicly known; one is under active attack.
The bug being abused in the wild is CVE-2019-0863, a Windows Error Reporting (WER) elevation of privilege vulnerability that exists in the way WER handles files. Attackers must first gain unprivileged execution on a victim system to execute an attack. "The exploitation of this vulnerability could lead to arbitrary code execution in kernel mode, which is typically reserved for trusted functions of the operating system," says Satnam Narang, senior research engineer at Tenable. Exploitation of CVE-2019-0863 would also let an attacker view, change, or delete data, or create new accounts with admin privileges.
"While details about the use of the exploit are not available, it is likely being used in limited attacks against specific targets," writes Dustin Childs of Trend Micro's Zero-Day Initiative.
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