CVE-2018-18751 in gettext
Summary
by MITRE
An issue was discovered in GNU gettext 0.19.8. There is a double free in default_add_message in read-catalog.c, related to an invalid free in po_gram_parse in po-gram-gen.y, as demonstrated by lt-msgfmt.
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Analysis
by VulDB Data Team • 06/03/2023
The vulnerability identified as CVE-2018-18751 represents a critical memory corruption flaw within GNU gettext version 0.19.8 that manifests through a double free condition during the processing of message catalog files. This issue occurs in the read-catalog.c component where the default_add_message function encounters a scenario that leads to improper memory management, specifically triggering a double free operation. The root cause extends to the po-gram-gen.y parser implementation where po_gram_parse function handles invalid memory deallocation during the parsing process of .po files. The vulnerability is particularly dangerous because it can be exploited through the lt-msgfmt utility, which is part of the GNU gettext build system and commonly used for processing translation catalogs. This double free condition creates a potential for arbitrary code execution or denial of service when the affected software processes maliciously crafted translation files.
The technical implementation of this vulnerability stems from improper memory handling within the GNU gettext parsing framework where memory allocated for message catalog entries is freed twice during the parsing lifecycle. When the po_gram_parse function processes grammar rules from the .po files, it fails to properly track memory allocation states, leading to situations where the same memory block gets deallocated multiple times. This memory management error creates a heap corruption condition that can be leveraged by attackers to manipulate program execution flow. The vulnerability specifically affects the default_add_message function in read-catalog.c which is responsible for adding parsed message entries to the catalog structure, making it a critical component in the exploitation chain.
The operational impact of CVE-2018-18751 extends beyond simple denial of service scenarios to potentially enable remote code execution in systems that process untrusted translation files. Since GNU gettext is widely used across various open source projects and operating systems for internationalization purposes, this vulnerability affects numerous applications that rely on proper message catalog handling. Attackers could exploit this by crafting malicious .po files that, when processed by lt-msgfmt or similar tools, trigger the double free condition. The vulnerability is particularly concerning in build environments where automated tools process translation catalogs, as these systems may be exposed to untrusted input from external sources. Systems using GNU gettext for localization may experience crashes, data corruption, or potentially arbitrary code execution depending on the exploitation context.
Mitigation strategies for CVE-2018-18751 should focus on immediate software updates to patched versions of GNU gettext that address the double free condition in both read-catalog.c and po-gram-gen.y components. Organizations should prioritize updating their GNU gettext installations to versions 0.19.9 or later where the memory management issues have been resolved. Additionally, input validation should be implemented at the application level to prevent processing of untrusted .po files, particularly in automated build environments. Security monitoring should be enhanced to detect unusual memory allocation patterns or crashes during message catalog processing. The vulnerability aligns with CWE-415 which describes double free conditions in memory management, and could potentially map to ATT&CK technique T1059.007 for execution through command-line interfaces where the vulnerable tools are invoked. Organizations should also consider implementing sandboxing mechanisms for translation processing tasks and maintaining strict access controls over systems that handle message catalog files to prevent unauthorized exploitation of this memory corruption vulnerability.