CVE-2019-19232 in macOS
Summary
by MITRE
** <A HREF="https://cve.mitre.org/about/faqs.html#disputed_signify_in_cve_entry">DISPUTED</A> ** In Sudo through 1.8.29, an attacker with access to a Runas ALL sudoer account can impersonate a nonexistent user by invoking sudo with a numeric uid that is not associated with any user. NOTE: The software maintainer believes that this is not a vulnerability because running a command via sudo as a user not present in the local password database is an intentional feature. Because this behavior surprised some users, sudo 1.8.30 introduced an option to enable/disable this behavior with the default being disabled. However, this does not change the fact that sudo was behaving as intended, and as documented, in earlier versions.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability described in CVE-2019-19232 pertains to a behavior in sudo versions through 1.8.29 that allows unauthorized impersonation of users through numeric uid values. This issue specifically affects systems where an attacker possesses a Runas ALL sudoer account, which grants them the ability to execute commands as any user. The technical flaw manifests when sudo processes numeric uid values that do not correspond to existing local user accounts, enabling the attacker to potentially bypass normal user authentication and authorization mechanisms.
This behavior represents a design decision that was intentionally implemented in sudo's architecture, as documented in the software's functionality. The vulnerability exists because sudo was designed to allow execution of commands as users specified by numeric uid values, even when those uids do not correspond to actual user accounts in the local password database. This design choice was maintained through version 1.8.29, creating a potential security risk for systems where such permissions are granted to less privileged users. The issue specifically impacts systems where the sudoers configuration allows Runas ALL permissions, which can be exploited by attackers who have already gained sufficient privileges to leverage this functionality.
The operational impact of this vulnerability extends beyond simple user impersonation, as it can enable attackers to potentially escalate privileges or execute commands with unexpected user contexts. When an attacker invokes sudo with a numeric uid that does not correspond to a real user, the system processes this command as intended by the software's design, rather than rejecting it as invalid. This behavior can be exploited in scenarios where the attacker has already established a foothold with Runas ALL permissions, potentially allowing them to execute commands under contexts that may have different permissions or access levels than the original user account. The vulnerability's impact is amplified in environments where multiple user accounts exist with varying permission levels, as the numeric uid impersonation can be used to access resources that would normally be restricted to specific user accounts.
The security community has debated the classification of this issue as a vulnerability, with the software maintainer asserting that this behavior was intentional and documented. This perspective aligns with CWE-250, which addresses "Execute Code with Unusual or Unconventional Privilege Level" and reflects the principle that software should behave according to its documented specifications. However, the issue was not widely recognized as a security concern until users encountered unexpected behavior in practice. The introduction of sudo 1.8.30 addressed this by providing administrators with explicit control over this behavior through configuration options, allowing them to disable the numeric uid impersonation feature. This change reflects the ATT&CK technique T1068, which involves exploiting the use of privileged accounts, and demonstrates how seemingly legitimate software features can be leveraged for unintended purposes when not properly controlled. Organizations should consider implementing strict sudoers configurations that limit Runas ALL permissions and ensure that numeric uid impersonation is disabled where it is not required for legitimate operational purposes.
The fundamental issue lies in the balance between software functionality and security expectations. While the behavior was documented and intentional, it surprised users who expected sudo to validate user existence before executing commands. This discrepancy between expected and actual behavior creates a security gap that attackers can exploit. The vulnerability highlights the importance of understanding the complete implications of software design decisions, particularly those involving privilege escalation and user authentication. Organizations should review their sudoers configurations to ensure that Runas ALL permissions are only granted to users who require such extensive privileges, and should consider implementing additional logging and monitoring to detect unusual numeric uid usage patterns. The issue also underscores the need for regular security assessments of system components to identify behaviors that may not align with security best practices, even when they are technically within the scope of documented functionality.