CVE-2015-6525 in libevent
Summary
by MITRE
Multiple integer overflows in the evbuffer API in Libevent 2.0.x before 2.0.22 and 2.1.x before 2.1.5-beta allow context-dependent attackers to cause a denial of service or possibly have other unspecified impact via "insanely large inputs" to the (1) evbuffer_add, (2) evbuffer_prepend, (3) evbuffer_expand, (4) exbuffer_reserve_space, or (5) evbuffer_read function, which triggers a heap-based buffer overflow or an infinite loop. NOTE: this identifier was SPLIT from CVE-2014-6272 per ADT3 due to different affected versions.
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Analysis
by VulDB Data Team • 03/10/2018
The vulnerability identified as CVE-2015-6525 represents a critical security flaw within the Libevent library's evbuffer API implementation. This issue affects versions 2.0.x prior to 2.0.22 and 2.1.x prior to 2.1.5-beta, creating a significant risk for systems that rely on this networking library for asynchronous event handling. The vulnerability stems from improper handling of integer overflow conditions during buffer management operations, which can be exploited by context-dependent attackers to disrupt system functionality or potentially achieve more severe consequences.
The technical flaw manifests through multiple functions within the evbuffer API including evbuffer_add, evbuffer_prepend, evbuffer_expand, evbuffer_reserve_space, and evbuffer_read. These functions fail to properly validate input parameters, particularly when processing "insanely large inputs" that exceed normal buffer size constraints. When attackers provide maliciously crafted inputs that trigger integer overflow conditions, the library's memory management mechanisms become compromised, leading to heap-based buffer overflows or infinite loop scenarios. The root cause aligns with CWE-190, which specifically addresses integer overflow conditions, and CWE-122, which covers heap-based buffer overflow vulnerabilities.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the potential for unspecified additional consequences makes it particularly dangerous for production environments. Systems utilizing Libevent for network communications, web servers, and application frameworks that depend on this library for event handling could experience complete service disruption through heap corruption or resource exhaustion. The infinite loop condition poses a particular risk as it can consume system resources indefinitely, potentially leading to system instability or complete system crashes. This vulnerability affects the foundational networking capabilities of applications, making it a critical concern for infrastructure providers and security teams.
Mitigation strategies should prioritize immediate patching of affected Libevent versions to the secure releases mentioned in the advisory. Organizations should implement comprehensive monitoring for unusual memory consumption patterns or service disruptions that might indicate exploitation attempts. Network segmentation and input validation controls can provide additional defense layers, while regular security assessments should verify that all components utilizing Libevent have been properly updated. The vulnerability's classification under ATT&CK technique T1499.004 for network denial of service and T1059.007 for command and scripting interpreter provides guidance for threat detection and response planning. System administrators should also consider implementing runtime protections and memory corruption detection mechanisms to identify and prevent exploitation attempts before they can cause significant damage to operational systems.