CVE-2013-2174 in cURL
Summary
by MITRE
Heap-based buffer overflow in the curl_easy_unescape function in lib/escape.c in cURL and libcurl 7.7 through 7.30.0 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted string ending in a "%" (percent) character.
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Analysis
by VulDB Data Team • 05/17/2021
The vulnerability identified as CVE-2013-2174 represents a critical heap-based buffer overflow affecting the cURL and libcurl libraries version 7.7 through 7.30.0. This flaw resides within the curl_easy_unescape function located in the lib/escape.c source file, demonstrating a classic memory corruption issue that can be exploited remotely. The vulnerability specifically manifests when processing crafted strings that end with a percent (%) character, creating a dangerous condition where the application's memory management becomes compromised. This type of vulnerability falls under CWE-121, which categorizes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution through memory corruption.
The technical implementation of this vulnerability exploits the improper handling of percent-encoded strings during URL decoding operations. When cURL processes a string ending with a percent character, the curl_easy_unescape function fails to properly validate the input length and buffer boundaries, leading to memory corruption that can result in either application crashes or more severe exploitation opportunities. The heap-based nature of the overflow indicates that the vulnerable code allocates memory on the heap and subsequently writes beyond allocated buffer boundaries, potentially overwriting adjacent memory structures including function pointers or return addresses. This memory corruption can be leveraged by attackers to redirect program execution flow or cause system instability.
The operational impact of CVE-2013-2174 extends beyond simple denial of service scenarios to include potential arbitrary code execution capabilities. Remote attackers can craft malicious input strings containing trailing percent characters that, when processed by vulnerable cURL implementations, trigger the buffer overflow condition. This vulnerability affects numerous applications and systems that rely on cURL for HTTP/HTTPS operations, including web browsers, network monitoring tools, and server applications that utilize libcurl for URL handling. The vulnerability's exploitation potential is particularly concerning because it requires minimal input complexity, making it an attractive target for automated exploitation tools. Systems using affected versions of cURL or libcurl are at risk of experiencing application crashes that could be used for denial of service attacks, or in more sophisticated scenarios, could allow remote code execution.
Mitigation strategies for CVE-2013-2174 primarily focus on immediate version upgrades to cURL 7.31.0 or later, which contain the necessary patches to address the heap-based buffer overflow. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing cURL or libcurl components are updated promptly. Additional defensive measures include input validation and sanitization at application boundaries, implementing strict boundary checks for string processing functions, and deploying intrusion detection systems to monitor for exploitation attempts. Security teams should also consider implementing network segmentation and access controls to limit exposure of vulnerable applications. The vulnerability highlights the importance of regular security assessments and code reviews focusing on memory management practices, particularly for libraries handling user-supplied data. Organizations should also establish procedures for monitoring security advisories and maintaining up-to-date vulnerability intelligence to prevent similar issues from affecting their infrastructure.