CVE-2019-20433 in Aspell
Summary
by MITRE
libaspell.a in GNU Aspell before 0.60.8 has a buffer over-read for a string ending with a single '\0' byte, if the encoding is set to ucs-2 or ucs-4 outside of the application, as demonstrated by the ASPELL_CONF environment variable.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 03/26/2024
The vulnerability identified as CVE-2019-20433 resides within the GNU Aspell library's libaspell.a component and affects versions prior to 0.60.8. This buffer over-read condition represents a critical security flaw that can potentially lead to arbitrary code execution or system instability when processing text encoded in UCS-2 or UCS-4 formats. The vulnerability specifically manifests when the application encounters a string that terminates with a single null byte character, creating an exploitable condition that bypasses normal input validation mechanisms. The flaw is particularly concerning because it can be triggered through environment variable manipulation, specifically via the ASPELL_CONF environment variable, which allows attackers to influence the library's behavior without direct program interaction.
The technical implementation of this vulnerability stems from improper boundary checking within the string processing functions of the Aspell library. When the library processes text with UCS-2 or UCS-4 encoding, it fails to properly validate the string boundaries before reading memory locations, leading to an over-read condition where the program attempts to access memory beyond the allocated buffer. This occurs specifically when a string ends with a single null byte character, which the library does not correctly handle during its internal parsing routines. The flaw is classified under CWE-125 as an "Out-of-bounds Read" and represents a classic buffer overflow vulnerability that can be exploited through improper input validation. The vulnerability's exploitation potential is amplified by the fact that it can be triggered through environment variable manipulation, making it accessible to attackers who can influence the application's runtime configuration.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially enable attackers to execute arbitrary code on affected systems. When an application using GNU Aspell processes input through the ASPELL_CONF environment variable, the library's failure to properly validate string boundaries can lead to information disclosure, denial of service, or even remote code execution depending on the system configuration. The vulnerability affects any system running GNU Aspell versions before 0.60.8 where applications may be subject to environment variable injection attacks. This creates a significant risk for server applications, web applications, and any software that relies on Aspell for spell checking functionality, particularly when these applications process untrusted input or are subject to environment variable manipulation by attackers.
Mitigation strategies for CVE-2019-20433 should prioritize the immediate upgrade to GNU Aspell version 0.60.8 or later, which contains the necessary patches to address the buffer over-read condition. System administrators should also implement strict environment variable validation and sanitization procedures to prevent unauthorized manipulation of the ASPELL_CONF variable. The implementation of proper input validation mechanisms within applications that utilize Aspell can provide additional defense-in-depth measures. Organizations should also consider implementing runtime monitoring and intrusion detection systems to identify potential exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving environment variable manipulation and privilege escalation through library injection, making it particularly relevant for defensive security operations. Additionally, the vulnerability highlights the importance of proper memory management practices and input validation, which should be incorporated into security development lifecycle processes to prevent similar issues in other software components.