CVE-2017-16997 in C Library
Summary
by MITRE
elf/dl-load.c in the GNU C Library (aka glibc or libc6) 2.19 through 2.26 mishandles RPATH and RUNPATH containing $ORIGIN for a privileged (setuid or AT_SECURE) program, which allows local users to gain privileges via a Trojan horse library in the current working directory, related to the fillin_rpath and decompose_rpath functions. This is associated with misinterpretion of an empty RPATH/RUNPATH token as the "./" directory. NOTE: this configuration of RPATH/RUNPATH for a privileged program is apparently very uncommon; most likely, no such program is shipped with any common Linux distribution.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/18/2023
The vulnerability identified as CVE-2017-16997 represents a critical privilege escalation flaw within the GNU C Library (glibc) affecting versions 2.19 through 2.26. This issue specifically targets how the dynamic loader handles RPATH and RUNPATH environment variables when they contain the $ORIGIN token in privileged programs. The flaw exploits a fundamental misinterpretation in the dl-load.c component where empty RPATH/RUNPATH tokens are incorrectly treated as equivalent to the "./" directory path, creating a dangerous security boundary that can be exploited by local attackers.
The technical mechanism behind this vulnerability involves the fillin_rpath and decompose_rpath functions within glibc's dynamic loading system. When a setuid or AT_SECURE program processes RPATH/RUNPATH containing $ORIGIN, the library fails to properly validate the empty token interpretation, allowing an attacker to place malicious shared libraries in the current working directory. This creates a scenario where the dynamic loader will prioritize loading these attacker-controlled libraries over legitimate system libraries, effectively bypassing security mechanisms designed to prevent such privilege escalation attacks. The vulnerability manifests because the system incorrectly resolves $ORIGIN to the current working directory when it should maintain proper security boundaries.
The operational impact of this vulnerability is significant for systems running affected glibc versions, particularly when executing privileged programs that utilize RPATH or RUNPATH with $ORIGIN tokens. Attackers can leverage this flaw to execute arbitrary code with elevated privileges, potentially gaining root access to compromised systems. The attack requires local access and the ability to place files in the current working directory of the target program, making it particularly dangerous in environments where users can write to directories where privileged programs execute. According to industry standards, this vulnerability maps to CWE-276, which specifically addresses improper privileges, and aligns with ATT&CK technique T1068, which covers privilege escalation through dynamic link library injection.
Mitigation strategies for CVE-2017-16997 focus on both immediate patching and configuration hardening. The primary solution involves upgrading to glibc version 2.27 or later where this vulnerability has been resolved through proper handling of RPATH/RUNPATH token interpretation. Organizations should also review and minimize the use of RPATH/RUNPATH with $ORIGIN tokens in privileged programs, as this configuration is uncommon and poses unnecessary risk. System administrators should implement strict file system permissions and monitoring to detect unauthorized library placements in directories where privileged programs execute. Additionally, the principle of least privilege should be enforced by avoiding unnecessary setuid bit usage and ensuring that programs requiring RPATH/RUNPATH functionality are properly secured against directory traversal attacks. The vulnerability's rarity in common distributions makes it less likely to be exploited broadly, but the potential impact remains severe for systems that do employ the affected configuration patterns.