CVE-2026-19880 in Logback-classic
Summary
by MITRE • 08/14/2026
Path-traversal vulnerability in QOS.CH Sarl Logback-classic on Java (logback-classic module) allows path-traversal vulnerability. More specifically, an MDC-based discriminator value flows unsanitized into a nested FileAppender path, letting an attacker who influences that MDC value (e.g. via an HTTP header) create and append log files outside the intended directory.
This issue affects Logback-classic: from 0.9.14 through 1.6.2.
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Analysis
by VulDB Data Team • 08/14/2026
This vulnerability represents a critical path traversal flaw in the logback-classic module of the Java logging framework, specifically affecting versions ranging from 0.9.14 through 1.6.2. The vulnerability stems from improper sanitization of MDC (Mapped Diagnostic Context) values within the discriminator configuration mechanism, creating an exploitable condition where attacker-controlled input can influence file system operations. The issue manifests when an MDC-based discriminator value flows unsanitized into a nested FileAppender path, allowing malicious actors to manipulate log file creation and appending behavior beyond intended directories.
The technical exploitation occurs through manipulation of MDC values that are typically populated from HTTP headers or other user-controllable inputs within web applications. When the logging framework processes these unsanitized discriminator values, it constructs file paths without proper validation or sanitization, enabling attackers to craft malicious input that traverses directory boundaries. This creates a scenario where log files can be written to arbitrary locations on the filesystem, potentially leading to unauthorized file creation, data exfiltration, or even system compromise through log injection attacks.
The operational impact of this vulnerability extends beyond simple path traversal, as it can enable attackers to create malicious log files that may be executed by log processing systems, inject false entries into audit trails, or manipulate application behavior through crafted log messages. The vulnerability affects the fundamental logging infrastructure of applications using affected versions, potentially compromising the integrity and confidentiality of system logs, which are critical for security monitoring and incident response activities. This issue aligns with CWE-22 Path Traversal and can be categorized under ATT&CK technique T1562.001 Impairing Defenses - Disable or Modify Tools, as it undermines the logging infrastructure that organizations rely upon for security operations.
Organizations should immediately update to logback-classic versions 1.7.0 or later, which include proper sanitization of discriminator values and path validation mechanisms. Additionally, administrators should implement strict input validation for MDC values, particularly those derived from HTTP headers, and consider implementing file system access controls that limit write permissions to logging directories. The vulnerability demonstrates the importance of validating all user-controllable inputs within logging frameworks and highlights the potential for seemingly benign configuration parameters to create security risks when combined with inadequate input sanitization practices.