CVE-2018-20721 in uriparser
Summary
by MITRE
URI_FUNC() in UriParse.c in uriparser before 0.9.1 has an out-of-bounds read (in uriParse*Ex* functions) for an incomplete URI with an IPv6 address containing an embedded IPv4 address, such as a "//[::44.1" address.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/01/2023
The vulnerability identified as CVE-2018-20721 resides within the uriparser library version 0.9.1 and earlier, specifically affecting the URI_FUNC() function located in UriParse.c. This flaw manifests as an out-of-bounds read condition that occurs during the parsing of incomplete URIs containing IPv6 addresses with embedded IPv4 addresses. The issue is particularly triggered when processing malformed URI strings such as those beginning with "//[::44.1", where the IPv6 address structure contains an embedded IPv4 component that creates parsing ambiguities. The vulnerability represents a classic buffer over-read scenario that can potentially lead to information disclosure or system instability.
The technical implementation of this vulnerability stems from insufficient input validation and boundary checking within the uriParseEx functions of the uriparser library. When the parser encounters an incomplete URI with an IPv6 address containing embedded IPv4 data, the parsing logic fails to properly validate the boundaries of the address components. This leads to the parser attempting to read memory locations beyond the allocated buffer boundaries, specifically when processing the transition between IPv6 and IPv4 address segments within the bracketed IPv6 address format. The flaw is categorized under CWE-125 as an out-of-bounds read, which occurs when a program reads data past the end of a valid buffer region. The parsing functions in question do not adequately handle malformed input sequences that contain embedded IPv4 addresses within IPv6 address brackets, causing the parser to traverse memory beyond intended boundaries.
The operational impact of this vulnerability extends beyond simple memory access violations to potentially enable more sophisticated attack vectors. An attacker could exploit this flaw by crafting malicious URI strings that trigger the out-of-bounds read condition, potentially leading to information disclosure through memory content leakage or causing application crashes that could result in denial of service. The vulnerability affects any application or system that relies on the uriparser library for URI parsing, including web browsers, web servers, and network applications that process user-supplied URI data. This makes the impact particularly significant in environments where untrusted URI input is processed, as demonstrated by the ATT&CK framework's categorization of such vulnerabilities under privilege escalation and denial of service tactics. The vulnerability's exploitation potential increases when considering that URI parsing is a fundamental operation in web applications, making it a prime target for attackers seeking to compromise system stability or extract sensitive information.
Mitigation strategies for CVE-2018-20721 primarily focus on upgrading to uriparser version 0.9.1 or later, where the out-of-bounds read issue has been addressed through improved input validation and boundary checking mechanisms. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing the uriparser library receive the necessary updates. Additionally, developers should consider implementing input sanitization layers that validate URI format before passing data to the parsing functions, though this approach represents a secondary defense mechanism. The vulnerability underscores the importance of robust boundary checking in parsing libraries and highlights the need for thorough testing of edge cases in network protocol implementations. Security teams should monitor for any potential exploitation attempts targeting this vulnerability and ensure that network applications employing uriparser are regularly updated to prevent exploitation attempts that could leverage the out-of-bounds read condition for information disclosure or service disruption attacks.