CVE-2021-29951 in Firefox ESR
Summary
by MITRE • 06/24/2021
The Mozilla Maintenance Service granted SERVICE_START access to BUILTIN|Users which, in a domain network, grants normal remote users access to start or stop the service. This could be used to prevent the browser update service from operating (if an attacker spammed the 'Stop' command); but also exposed attack surface in the maintenance service. *Note: This issue only affected Windows operating systems older than Win 10 build 1709. Other operating systems are unaffected.*. This vulnerability affects Thunderbird < 78.10.1, Firefox < 87, and Firefox ESR < 78.10.1.
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Analysis
by VulDB Data Team • 06/24/2021
The Mozilla Maintenance Service vulnerability represents a critical privilege escalation issue that emerged from improper access control implementation within Windows service management. This flaw specifically affected Windows operating systems prior to version 1709, where the maintenance service was configured with overly permissive permissions that granted BUILTIN|Users group membership the ability to start and stop the service. The security implications of this misconfiguration stem from the fundamental principle of least privilege violation, where standard domain users were granted capabilities typically reserved for administrative functions within the Windows security model.
The technical nature of this vulnerability resides in the Windows Service Control Manager's permission system where the maintenance service was configured with SERVICE_START access rights for the BUILTIN|Users group. This configuration allowed any authenticated user on the network to manipulate the service state through standard Windows service control mechanisms. The vulnerability operates at the intersection of Windows security model implementation and application-level service management, creating an attack surface that could be leveraged for both denial-of-service and potential privilege escalation scenarios. According to CWE-269, this represents a privilege escalation vulnerability through improper privileges assignment, while the ATT&CK framework categorizes this under T1059.001 for execution through Windows service manipulation.
The operational impact of this vulnerability extended beyond simple service disruption to create potential security compromise opportunities within enterprise environments. Attackers could exploit this flaw by repeatedly issuing stop commands to prevent Mozilla's browser update service from functioning properly, effectively disabling automatic security updates and leaving systems vulnerable to known exploits. Additionally, the broad access permissions created opportunities for attackers to manipulate other aspects of the maintenance service functionality that might have been exposed through the service interface, potentially leading to more sophisticated attack vectors within the browser ecosystem. The vulnerability affected multiple Mozilla products including Firefox versions prior to 87, Thunderbird versions prior to 87, and Firefox ESR versions prior to 78.10.1, indicating a widespread impact across the organization's software portfolio.
Mitigation strategies for this vulnerability required immediate patch deployment as the primary solution, with system administrators implementing the updated Mozilla software versions that corrected the service permission configuration. Organizations should also implement additional monitoring of service state changes within their Windows environments to detect unauthorized manipulation of critical services. The remediation process involved reviewing and correcting service permissions through Windows Group Policy configurations, ensuring that only appropriate user groups maintained access to service control functions. Security teams should also conduct comprehensive audits of all Windows services to identify similar permission misconfigurations that might exist within their infrastructure, as this vulnerability highlighted the importance of proper service security hardening practices across enterprise environments.