CVE-2026-49846 in libks
Summary
by MITRE • 09/11/2026
libks provides foundational support for signalwire C products. Prior to version 2.0.11, `clean_uri()` in libks's HTTP request parser fails to reject URIs whose path has more segments than its internal canonicalization buffer can hold. The canonicalization step silently passes such URIs through with embedded ".." sequences intact, enabling path traversal in any consumer that later joins the URI with a filesystem path. Version 2.0.11 patches the issue.
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Analysis
by VulDB Data Team • 09/11/2026
The vulnerability identified within libks versions prior to 2.0.11 represents a critical failure in input validation and canonicalization logic, specifically located within the clean_uri function of its HTTP request parser component. LibKS serves as a foundational library for SignalWire C products, providing essential utilities for network communication and data processing. The core technical flaw stems from an insufficient buffer size check during the URI normalization process. When parsing Uniform Resource Identifiers, the internal canonicalization routine is designed to resolve relative path components such as dot-dot sequences to ensure safe handling of file paths or resource locations. However, in affected versions, if a supplied URI contains more hierarchical segments than can fit into the fixed-size internal buffer used for this operation, the function does not reject the input nor truncate it safely. Instead, it silently passes the malformed URI through with embedded dot-dot sequences intact and unresolved.
This behavior creates a direct pathway for path traversal attacks against any application or service that consumes libks and subsequently joins these URIs with local filesystem paths. An attacker can craft HTTP requests containing deeply nested directory traversal patterns that exceed the buffer limit, thereby bypassing canonicalization checks designed to prevent access outside of intended directories. Because the vulnerability occurs at the parsing level before higher-level security controls are applied, it allows malicious actors to read sensitive files, execute arbitrary code via included configuration or script files, or potentially achieve remote code execution depending on how the consuming application handles the resulting file paths. This is particularly dangerous in web server contexts where such libraries might be used to map URLs to static assets or API endpoints mapped to disk locations.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-22 Path Traversal: '..' Sequence. The failure to properly sanitize user-supplied input before processing it constitutes an improper restriction of a pathname to a restricted directory, which is the defining characteristic of path traversal vulnerabilities. In terms of offensive security frameworks, this flaw facilitates techniques associated with ATT&CK T1083 File and Directory Discovery or more specifically T1564 Hidden Files and Directories if used for evasion, but primarily it enables lateral movement through file system access as described in T1083 when combined with other exploitation steps. The silent failure mode is particularly insidious because standard logging mechanisms may not immediately flag the anomaly since no error code is returned to the caller, allowing attackers to probe and exploit the condition without triggering immediate alerts based on parser errors.
The operational impact of this vulnerability extends beyond simple data exfiltration. In environments where libks is integrated into high-traffic services or critical infrastructure components managed by SignalWire products, successful exploitation could lead to complete compromise of underlying systems hosting these applications. Attackers can leverage the path traversal capability to access configuration files containing credentials, database connection strings, or private keys stored in accessible directories relative to the web root or application working directory. Furthermore, if the consuming application writes data based on parsed URI segments without additional validation, it could lead to arbitrary file write vulnerabilities, allowing for persistent backdoor installation or system modification. The lack of explicit error handling means that developers relying on libks may assume all URIs are safely canonicalized, leading to a false sense of security in their own access control implementations.
Mitigation strategies must prioritize immediate upgrading to version 2.0.11 or later, where the internal buffer limits have been corrected and input validation has been strengthened to reject oversized URI paths explicitly. For organizations unable to patch immediately due to dependency constraints, defensive coding practices should be implemented at the application layer consuming libks. This includes implementing strict allow-listing for URL patterns rather than relying solely on canonicalization functions, validating path lengths against known safe limits before passing URIs to library functions, and ensuring that any file system operations derived from URI parsing are sandboxed or restricted using chroot environments or containerized deployments with minimal filesystem permissions. Additionally, security monitoring should be enhanced to detect anomalous HTTP requests containing excessive dot-dot sequences or unusually long URL paths, which serve as strong indicators of path traversal attempts targeting this specific vulnerability class. Regular audits of third-party library usage and integration points are essential to ensure that foundational components like libks do not introduce systemic weaknesses into the broader application architecture.