CVE-2018-7186 in Leptonica
Summary
by MITRE
Leptonica before 1.75.3 does not limit the number of characters in a %s format argument to fscanf or sscanf, which allows remote attackers to cause a denial of service (stack-based buffer overflow) or possibly have unspecified other impact via a long string, as demonstrated by the gplotRead and ptaReadStream functions.
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Analysis
by VulDB Data Team • 02/08/2023
The vulnerability identified as CVE-2018-7186 affects Leptonica version 1.75.3 and earlier, representing a critical stack-based buffer overflow flaw that stems from insufficient input validation within string parsing operations. This vulnerability specifically targets the fscanf and sscanf functions where format specifiers containing %s are used without proper character limits, creating an exploitable condition that can be triggered through malformed input data.
The technical implementation of this vulnerability occurs when the gplotRead and ptaReadStream functions process user-supplied input streams without enforcing maximum character limits for string format arguments. When these functions encounter a long string that exceeds the allocated buffer space on the stack, the excess data overflows into adjacent memory locations, potentially corrupting program execution flow and leading to denial of service conditions. The flaw resides in the improper handling of format strings that do not restrict the number of characters read, allowing attackers to supply arbitrarily long input sequences that exceed the intended buffer boundaries.
This vulnerability demonstrates characteristics consistent with CWE-121 Stack-based Buffer Overflow, where insufficient bounds checking in format string operations creates opportunities for memory corruption. The operational impact extends beyond simple denial of service to potentially enable arbitrary code execution depending on memory layout and exploitation conditions. Attackers can remotely trigger this vulnerability by crafting malicious input files that contain excessively long strings, making it particularly dangerous in networked environments where Leptonica is used to process external data sources.
The attack surface for CVE-2018-7186 encompasses any application or system that utilizes Leptonica libraries for image processing and data parsing, particularly those handling user-provided or network-based input streams. This includes document processing systems, image analysis tools, and any software that relies on Leptonica's gplot and pta stream reading capabilities. The vulnerability can be exploited through various attack vectors including file upload mechanisms, network protocols, or any interface that allows untrusted data to flow into the affected functions.
Mitigation strategies for this vulnerability require immediate patching of Leptonica libraries to version 1.75.3 or later, which implements proper bounds checking for format string operations. Organizations should also implement input validation measures at application layers that process data before it reaches Leptonica functions, including character limit enforcement and sanitization routines. Additionally, defensive programming practices such as using safer string handling functions like fgets instead of scanf family functions, combined with proper buffer size validation and stack canary implementations, can significantly reduce the risk of exploitation. The remediation aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as attackers may leverage such vulnerabilities to execute malicious code through compromised processing pipelines.