CVE-2018-19052 in lighttpd
Summary
by MITRE
An issue was discovered in mod_alias_physical_handler in mod_alias.c in lighttpd before 1.4.50. There is potential ../ path traversal of a single directory above an alias target, with a specific mod_alias configuration where the matched alias lacks a trailing '/' character, but the alias target filesystem path does have a trailing '/' character.
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Analysis
by VulDB Data Team • 06/05/2023
The vulnerability identified as CVE-2018-19052 represents a directory traversal flaw within the lighttpd web server's mod_alias module, specifically affecting versions prior to 1.4.50. This issue manifests in the physical handler component of mod_alias.c, where improper path resolution logic creates an exploitable condition that allows attackers to access files outside the intended alias directory boundaries. The vulnerability is particularly concerning as it demonstrates how seemingly minor configuration inconsistencies can lead to significant security implications in web server implementations.
The technical flaw occurs when lighttpd processes alias configurations where the matched alias pattern does not include a trailing forward slash character, but the target filesystem path for that alias does contain a trailing slash. This mismatch in path specification creates a condition where the path traversal logic fails to properly sanitize or validate the resolved path, allowing an attacker to navigate one directory level upward from the intended alias target. The vulnerability specifically exploits the interaction between the alias matching mechanism and the physical file system resolution, where the trailing slash in the target path causes the server to interpret the request differently than intended.
Operationally, this vulnerability enables unauthorized access to files and directories that should be restricted by the alias configuration, potentially allowing attackers to read sensitive files, access configuration data, or even execute arbitrary code if the server has appropriate permissions. The impact is particularly severe in environments where lighttpd serves content with strict access controls, as attackers could bypass these protections through carefully crafted requests that exploit the path traversal condition. This type of vulnerability aligns with CWE-22 Path Traversal and represents a classic example of how improper input validation and path resolution can lead to privilege escalation and information disclosure.
The security implications extend beyond simple file access, as this vulnerability can be leveraged in combination with other attack vectors to compromise entire web server installations. Attackers can construct requests that appear to target specific alias paths but actually traverse to unintended locations, potentially accessing system files, user data, or application configuration files that contain sensitive information. This vulnerability is particularly dangerous in shared hosting environments or when lighttpd is configured with aliases pointing to directories with broader permissions than intended. Mitigation efforts should focus on upgrading to lighttpd version 1.4.50 or later, where the path traversal logic has been corrected, and implementing proper configuration validation to ensure consistent trailing slash handling in alias definitions. Additionally, administrators should review all alias configurations to eliminate potential mismatched trailing slash scenarios that could enable similar vulnerabilities.