Attackers exploiting zero-day vulnerability in Windows Installer — Here’s what you need to know and Talos’ coverage
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-41379 | Local Privilege Escalation in Microsoft Windows Installer (CVE-2021-41379) CVE-2021-41379 is an elevation of privilege flaw in the Microsoft Windows Installer service, rooted in improper link resolution before file access (CWE-59), where the privileged installer can be made to follow attacker-controlled file links. It is triggered by a local, low-privileged user who initiates a Windows Installer operation and manipulates the links or paths the installer resolves while running with elevated rights. A successful attacker gains elevated (SYSTEM-level) privileges on the affected machine, a common post-breach step in ransomware chains. The affected list spans essentially the entire supported Windows install base: Windows 7, 8.1 and RT 8.1, Windows 10 versions 1507 through 21H1, Windows 11 21H2, and Windows Server 2004. Exploitation is confirmed in the wild - CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2022-03-03 with known ransomware use, and EPSS places it in the 97th percentile (19.4% probability of exploitation in 30 days) despite no public PoC being known. Do: Apply Microsoft's security update for CVE-2021-41379 (delivered via the November 2021 monthly Windows cumulative updates) to all affected Windows 7/8.1/RT 8.1/10/11 and Windows Server systems and keep cumulative updates current. Because CISA's KEV entry cites known ransomware use and the flaw is exploitable by any local standard user, prioritize patching multi-user hosts, servers, and endpoints that allow standard (non-admin) logons; as an interim mitigation, restrict local logon rights on unpatched machines and ensure users operate without administrative privileges. | 5.5 | 20% | KEV ransomware |
| mass≈1 billion+ Windows installations (effectively the entire supported Windows client and server install base) |
Full article292 words · extracted from blog.talosintelligence.com · click to collapse
Tuesday, November 23, 2021 13:29
Cisco Talos is releasing new SNORTⓇ rules to protect against the exploitation of a zero-day elevation of privilege vulnerability in Microsoft Windows Installer. This vulnerability allows an attacker with a limited user account to elevate their privileges to become an administrator. This vulnerability affects every version of Microsoft Windows, including fully patched Windows 11 and Server 2022. Talos has already detected malware samples in the wild that are attempting to take advantage of this vulnerability.
Microsoft released an update that was intended to fix CVE-2021-41379 on Nov. 9 as part of its monthly security update. Security researcher Abdelhamid Naceri initially discovered this elevation of privilege vulnerability and worked with Microsoft to address it. However, the patch released by Microsoft was not sufficient to remediate the vulnerability, andNaceri published proof-of-concept exploit code on GitHub on Nov. 22 that works despite the fixes implemented by Microsoft. The code Naceri released leverages the discretionary access control list (DACL) for Microsoft Edge Elevation Service to replace any executable file on the system with an MSI file, allowing an attacker to run code as an administrator.
Although Microsoft initially scored this as a medium- severity vulnerability, having a base CVSS score of 5.5, and a temporal score of 4.8, the release of functional proof-of-concept exploit code will certainly drive additional abuse of this vulnerability. As of the publication of this blog, there is no patch available from Microsoft.
Snort rule SIDs 58635 and 58636 will keep users protected from exploitation of this vulnerability. Cisco Secure Firewall customers should use the latest update to their ruleset by updating their SRU. Open-source Snort Subscriber Rule Set customers can stay up to date by downloading the latest rule pack available for purchase on Snort.org.
Text extracted automatically; images, tables and formatting may be missing. Original: https://blog.talosintelligence.com/attackers-exploiting-zero-day/