CVE-2017-7476 in Gnulib
Summary
by MITRE
Gnulib before 2017-04-26 has a heap-based buffer overflow with the TZ environment variable. The error is in the save_abbr function in time_rz.c.
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Analysis
by VulDB Data Team • 12/02/2022
The vulnerability identified as CVE-2017-7476 represents a critical heap-based buffer overflow within the gnulib library, specifically affecting versions prior to the 2017-04-26 release. This flaw resides in the save_abbr function within the time_rz.c file, which handles timezone-related operations in applications that utilize the GNU autotools infrastructure. The issue manifests when the TZ environment variable is processed, creating a scenario where maliciously crafted timezone specifications can trigger unauthorized memory access patterns.
The technical implementation of this vulnerability stems from inadequate bounds checking during the parsing of timezone abbreviations within the save_abbr function. When applications using gnulib process timezone data through the TZ environment variable, the library fails to validate the length of timezone abbreviation strings against allocated buffer boundaries. This oversight allows attackers to supply overly long timezone strings that exceed the allocated heap memory space, resulting in memory corruption that can be exploited for arbitrary code execution or denial of service conditions.
From an operational perspective, this vulnerability impacts any software system that relies on gnulib for timezone handling and utilizes the TZ environment variable for time zone configuration. The attack surface includes operating systems, network services, embedded devices, and applications built with GNU autotools that process user-provided timezone data. The vulnerability is particularly concerning because it can be triggered through environment variable manipulation without requiring direct user interaction, making it an attractive target for remote exploitation in networked applications.
The security implications of CVE-2017-7476 align with CWE-121, which categorizes heap-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for command and script injection through environment variables. The vulnerability's exploitation potential extends beyond simple denial of service to include privilege escalation scenarios where attackers can manipulate memory layout to achieve code execution. This makes it particularly dangerous in multi-tenant environments or systems where untrusted input might be processed through timezone handling functions.
Mitigation strategies for this vulnerability require immediate patching of affected gnulib versions to the 2017-04-26 release or later, which includes proper bounds checking in the save_abbr function. System administrators should also implement environment variable sanitization measures, particularly for applications that do not require complex timezone handling, and consider restricting TZ environment variable usage in security-sensitive contexts. Additionally, organizations should conduct vulnerability assessments to identify applications built with vulnerable gnulib versions and ensure comprehensive testing of timezone handling functionality in their software supply chains.