CVE-2019-17544 in Aspell
Summary
by MITRE
libaspell.a in GNU Aspell before 0.60.8 has a stack-based buffer over-read in acommon::unescape in common/getdata.cpp via an isolated \ character.
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Analysis
by VulDB Data Team • 01/08/2024
The vulnerability identified as CVE-2019-17544 affects GNU Aspell version 0.60.8 and earlier, specifically within the libaspell.a library component. This issue manifests as a stack-based buffer over-read that occurs during the processing of escaped character sequences, particularly when encountering isolated backslash characters. The flaw is located in the common::unescape function within the common/getdata.cpp source file, making it a critical component of the software's text processing pipeline vulnerable to malicious input manipulation.
The technical nature of this vulnerability stems from improper boundary checking during string parsing operations. When GNU Aspell encounters a backslash character that is not properly followed by a valid escape sequence, the unescape function attempts to access memory beyond the allocated buffer boundaries. This over-read condition can lead to information disclosure, application instability, or potentially more severe consequences depending on the execution context. The vulnerability specifically triggers when an isolated \ character is processed without proper validation of subsequent characters, creating a scenario where the parser reads beyond intended memory limits.
From an operational perspective, this vulnerability presents significant risks to systems that rely on GNU Aspell for text processing, spell checking, or natural language analysis. Attackers could potentially exploit this weakness by crafting malicious input containing isolated backslash characters, leading to denial of service conditions or information leakage from the application's memory space. The impact extends beyond simple application crashes, as the over-read behavior may expose sensitive data from adjacent memory locations, potentially including cryptographic keys, user credentials, or other confidential information. This vulnerability aligns with CWE-126, which describes buffer over-read conditions that can result in information exposure and system instability.
The exploitability of this vulnerability is enhanced by the fact that it occurs during routine text processing operations, meaning that any application or service using GNU Aspell as a dependency could be affected. The ATT&CK framework categorizes this as a memory corruption technique that can be leveraged for privilege escalation or information gathering. Organizations using GNU Aspell in web applications, email systems, or any text processing pipeline should consider this vulnerability as a potential attack vector. The remediation approach requires updating to GNU Aspell version 0.60.8 or later, where the buffer over-read condition has been addressed through proper input validation and boundary checking mechanisms.
This vulnerability demonstrates the importance of robust input validation in text processing libraries, particularly those handling escape sequences and character encoding. The flaw highlights the need for comprehensive testing of edge cases in parsing functions, especially those dealing with special characters and their combinations. Security practitioners should implement monitoring for unusual memory access patterns and ensure that all text processing components undergo thorough security review. The fix implemented in the updated version addresses the root cause by enforcing proper bounds checking and validating escape sequence completeness before attempting memory access operations, thereby preventing the stack-based buffer over-read condition from occurring.