CVE-2019-11072 in lighttpd
Summary
by MITRE
lighttpd before 1.4.54 has a signed integer overflow, which might allow remote attackers to cause a denial of service (application crash) or possibly have unspecified other impact via a malicious HTTP GET request, as demonstrated by mishandling of /%2F? in burl_normalize_2F_to_slash_fix in burl.c.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2019-11072 affects lighttpd versions prior to 1.4.54 and represents a critical signed integer overflow condition that can be exploited remotely to cause denial of service or potentially more severe impacts. This flaw exists within the HTTP request processing logic of the web server, specifically in how it handles certain URL encoding patterns. The vulnerability manifests when processing maliciously crafted HTTP GET requests that contain specific combinations of percent-encoded characters, particularly the sequence /%2F? which triggers improper handling within the burl_normalize_2F_to_slash_fix function located in the burl.c source file.
The technical implementation of this vulnerability stems from a flaw in integer arithmetic handling where a signed integer overflow occurs during URL normalization operations. When lighttpd encounters the specific pattern /%2F? in incoming HTTP requests, the server attempts to normalize the URL path by converting certain sequences, but the mathematical operations involved in this normalization process fail to properly validate integer boundaries. This overflow condition can result in unexpected behavior where the server's internal state becomes corrupted, leading to application crashes or potentially more dangerous memory corruption scenarios that could be exploited for additional attacks. The vulnerability is particularly concerning because it can be triggered through standard HTTP GET requests without requiring any authentication or special privileges from the attacker.
From an operational perspective, this vulnerability presents significant risk to web server availability and system stability, as remote attackers can reliably cause denial of service conditions simply by sending malformed requests to the affected lighttpd servers. The impact extends beyond mere service disruption since integer overflows in web server software can potentially lead to more serious consequences including arbitrary code execution or information disclosure if the overflow affects memory layout or control flow. The vulnerability affects systems that rely on lighttpd as their web server implementation, particularly those in environments where service availability is critical, such as web hosting platforms, content delivery networks, or applications with high traffic volumes where a single exploited vulnerability could cause widespread service degradation.
The mitigation strategy for CVE-2019-11072 involves immediate upgrading to lighttpd version 1.4.54 or later, which contains the necessary patches to address the signed integer overflow condition. Organizations should also implement network-level protections such as web application firewalls that can detect and block malicious HTTP requests containing the specific problematic patterns, though this approach provides only partial protection and should not replace the core patching effort. Security monitoring should be enhanced to detect unusual patterns of service disruption or application crashes that might indicate exploitation attempts, and system administrators should conduct thorough vulnerability assessments to ensure all lighttpd installations are properly updated. This vulnerability aligns with CWE-190, which describes signed integer overflow conditions, and represents a typical example of how integer arithmetic errors can lead to serious security implications in network services. The ATT&CK framework categorizes this as a denial of service attack technique that can be executed through network protocols, potentially leading to more advanced exploitation if combined with other vulnerabilities or attack vectors.