CVE-2007-1030 in libevent
Summary
by MITRE
Niels Provos libevent 1.2 and 1.2a allows remote attackers to cause a denial of service (infinite loop) via a DNS response containing a label pointer that references its own offset.
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Analysis
by VulDB Data Team • 06/09/2025
The vulnerability described in CVE-2007-1030 represents a critical denial of service flaw within the libevent library version 1.2 and 1.2a developed by Niels Provos. This issue specifically affects the library's DNS resolution handling mechanism, where the software fails to properly validate DNS response structures during asynchronous network operations. The vulnerability stems from insufficient input validation and lacks proper bounds checking when processing DNS label pointers, creating a condition where maliciously crafted DNS responses can trigger unexpected behavior in the event loop processing.
The technical flaw manifests when a DNS response contains a label pointer that references its own offset, creating a circular reference within the DNS name resolution process. This condition causes the libevent library to enter an infinite loop during DNS response parsing, as the pointer traversal mechanism continuously follows the same reference without termination. The vulnerability operates at the protocol parsing layer where DNS name compression is implemented, specifically targeting the mechanism used to handle label pointers that reference offsets within the DNS message structure. This type of flaw falls under CWE-129, which addresses improper validation of the length or size of input data, and more specifically relates to CWE-691, which covers insufficient control of a resource through a mechanism that allows access to a resource without proper authorization.
The operational impact of this vulnerability is significant for systems utilizing libevent for network operations, particularly those that rely on asynchronous DNS resolution. Attackers can exploit this weakness by crafting malicious DNS responses that contain self-referential label pointers, causing the target system to consume excessive CPU resources and potentially leading to complete service unavailability. The infinite loop consumes system resources continuously, making it difficult to distinguish from other resource exhaustion attacks, and can affect any application that uses libevent for handling network events, including web servers, proxy services, and network monitoring tools. This vulnerability directly aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and can be classified under the broader category of resource exhaustion attacks that target application logic rather than network bandwidth.
Systems that implement libevent version 1.2 or 1.2a for DNS resolution and asynchronous network handling are at risk, particularly those in environments where DNS queries are processed without additional validation layers. The vulnerability can be exploited by remote attackers who control DNS servers or have the ability to intercept DNS responses, making it particularly dangerous in network environments where DNS traffic is not properly validated or filtered. Organizations should consider implementing network segmentation, DNS filtering mechanisms, and monitoring for unusual CPU consumption patterns as part of their defensive strategy. The recommended mitigation involves upgrading to libevent version 1.3 or later, which includes proper validation of DNS label pointer references and prevents circular traversal conditions. Additionally, implementing DNS response validation at the network level and applying rate limiting for DNS queries can help reduce the impact of such attacks while maintaining service availability.