CVE-2007-4135 in nfsidmap
Summary
by MITRE
The NFSv4 ID mapper (nfsidmap) before 0.17 does not properly handle return values from the getpwnam_r function when performing a username lookup, which can cause it to report a file as being owned by "root" instead of "nobody" if the file exists on the server but not on the client.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability described in CVE-2007-4135 affects the Network File System version 4 ID mapper component known as nfsidmap, which is responsible for mapping user and group names to their corresponding numeric identifiers in NFSv4 environments. This flaw exists in versions prior to 0.17 of the nfsidmap utility and represents a significant security concern within distributed file systems where user identity mapping is critical for access control and file ownership verification. The issue stems from improper error handling within the username lookup mechanism that directly impacts how file ownership is reported and interpreted within NFSv4 networks.
The technical root cause of this vulnerability lies in the improper handling of return values from the getpwnam_r function, which is a reentrant version of the getpwnam function used for retrieving user information from the system's user database. When nfsidmap performs a username lookup for a user that exists on the NFS server but not on the client system, the getpwnam_r function may return an error code or incomplete data. However, the nfsidmap implementation fails to properly check these return values and instead defaults to reporting the file as owned by "root" rather than the correct "nobody" user identifier. This misreporting occurs because the software does not adequately validate the success of the username resolution process before making assumptions about user ownership.
The operational impact of this vulnerability extends beyond simple misreporting of file ownership attributes, potentially creating security implications within NFSv4 environments where access controls and user permissions are strictly enforced. When files are incorrectly reported as owned by "root" instead of "nobody," it can lead to confusion in permission checking mechanisms and may allow unauthorized access to files that should be restricted to specific user contexts. This behavior particularly affects systems where the "nobody" user is used as a default for anonymous or unauthenticated access, and where proper ownership reporting is essential for maintaining security boundaries. The vulnerability essentially creates a false positive in user ownership determination that could be exploited to bypass certain access control checks or confuse administrators during security audits.
This vulnerability aligns with CWE-252, which addresses improper checking of return values, and demonstrates how inadequate error handling can lead to security-relevant behavior in system utilities. The issue also relates to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation,' as improper user identification could potentially be leveraged to gain elevated access rights through misconfigured permissions. The flaw represents a classic case of insufficient input validation and error handling in system-level components, where the failure to properly validate function return codes results in incorrect security state reporting. Organizations using NFSv4 implementations should prioritize updating their nfsidmap components to version 0.17 or later to address this vulnerability, as it could potentially be exploited to manipulate file ownership reporting in ways that compromise the security posture of distributed file systems. The vulnerability underscores the importance of proper error handling in security-critical system utilities and demonstrates how seemingly minor implementation flaws can have significant security implications in networked file systems.