CVE-2017-13743 in Liblouis
Summary
by MITRE
There is a buffer overflow in Liblouis 3.2.0, triggered in the function _lou_showString() in utils.c, that will lead to a remote denial of service attack.
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Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified in Liblouis version 3.2.0 represents a critical memory safety flaw located within the utility module, specifically inside the lou showString function found in utils.c. This buffer overflow condition arises from improper handling of input data during string processing operations. When the application processes certain character sequences or specific formatting instructions intended for display conversion, it fails to adequately validate the length of the incoming data against the allocated memory buffers. Consequently, if an attacker supplies a crafted input that exceeds the expected bounds, the excess data overwrites adjacent memory locations on the stack or heap, depending on the internal implementation details of the function at that specific version. This type of error is classically categorized under CWE-120, which denotes Buffer Copy without Checking Size of Input, and often intersects with CWE-787 for Out-of-bounds Write vulnerabilities when the overflow results in writing to memory regions outside the intended buffer boundaries.
The operational impact of this vulnerability is primarily centered on service availability rather than immediate code execution or privilege escalation, although the potential for exploitation extends beyond simple denial of service depending on the context and compiler protections enabled at compile time. In a typical deployment scenario where Liblouis is utilized by assistive technologies such as screen readers to convert Braille codes into text or vice versa, an attacker could exploit this flaw by sending specially crafted Braille input data through any interface that accepts user-provided strings for display purposes. The immediate consequence of triggering the overflow is typically a segmentation fault or application crash, leading to a remote denial of service attack. This disrupts the workflow for users relying on these assistive tools and can cause instability in host applications that integrate Liblouis as a library component. While the primary reported impact is availability loss, memory corruption vulnerabilities inherently carry risks related to information disclosure if sensitive data resides in adjacent memory regions or potential code execution if an attacker can precisely control the overwritten pointers and bypass modern mitigations such as stack canaries, ASLR, and DEP/NX bits.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1498, Network Denial of Service, specifically under sub-techniques involving resource exhaustion or application crashes via malformed input. The attack vector is considered remote if the vulnerable function is exposed through network services or APIs that process untrusted data from external sources. However, it may also be classified as local if the vulnerability requires user interaction to trigger within a desktop environment where an attacker has access to run applications with elevated privileges. The lack of rigorous bounds checking in utility functions like lou showString highlights a common oversight in legacy C codebases where performance optimization sometimes supersedes security validation during string manipulation routines.
Mitigation strategies for this vulnerability involve both immediate patching and long-term architectural improvements. The most effective remediation is to upgrade Liblouis to a version later than 3.2.0, assuming the maintainers have released patches that implement proper input length verification before copying data into fixed-size buffers. Developers should ensure that all string operations utilize safe alternatives or explicitly check buffer sizes using functions like strncpy_s or equivalent secure coding practices mandated by standards such as CERT C Coding Standard section STR37-C regarding bounds checking for strings. Additionally, integrating static analysis tools and dynamic fuzzing during the software development lifecycle can help detect similar out-of-bounds write conditions before deployment. For organizations unable to patch immediately due to dependency constraints, deploying web application firewalls or input validation layers at the network perimeter may filter malformed requests that trigger this specific overflow condition, although such controls are less reliable than direct code remediation.