CVE-2017-17484 in International Components for Unicode
Summary
by MITRE
The ucnv_UTF8FromUTF8 function in ucnv_u8.cpp in International Components for Unicode (ICU) for C/C++ through 60.1 mishandles ucnv_convertEx calls for UTF-8 to UTF-8 conversion, which allows remote attackers to cause a denial of service (stack-based buffer overflow and application crash) or possibly have unspecified other impact via a crafted string, as demonstrated by ZNC.
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Analysis
by VulDB Data Team • 01/26/2021
The vulnerability identified as CVE-2017-17484 affects the International Components for Unicode (ICU) library version 60.1 and earlier, specifically within the ucnv_UTF8FromUTF8 function located in ucnv_u8.cpp. This flaw represents a critical security issue that manifests during UTF-8 to UTF-8 conversion operations through the ucnv_convertEx API call. The vulnerability stems from improper handling of conversion parameters and buffer management when processing Unicode strings, creating a scenario where malicious input can trigger unexpected behavior in applications that rely on ICU for internationalization support.
The technical implementation of this vulnerability involves a stack-based buffer overflow condition that occurs when the ucnv_UTF8FromUTF8 function processes certain malformed UTF-8 sequences. When a crafted string is passed through the ucnv_convertEx function for UTF-8 to UTF-8 conversion, the function fails to properly validate input boundaries and buffer sizes, leading to memory corruption. This overflow can result in application crashes, making it a reliable denial of service vector. The vulnerability is particularly dangerous because it can be triggered remotely through user input processed by applications using ICU libraries, without requiring special privileges or complex attack vectors.
The operational impact of CVE-2017-17484 extends beyond simple service disruption to potentially enable more sophisticated attacks depending on the application context. When exploited, this vulnerability can cause applications to crash repeatedly, effectively rendering them unavailable to legitimate users. The potential for unspecified other impacts suggests that in certain configurations or with additional exploitation techniques, attackers might be able to achieve arbitrary code execution or information disclosure. Applications that process user-provided text, such as chat servers, web applications, or messaging platforms like ZNC mentioned in the vulnerability description, become particularly vulnerable to this type of attack.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses situations where data written to a stack buffer exceeds the buffer's allocated size, leading to memory corruption. From an adversarial perspective, this flaw maps to several ATT&CK tactics including privilege escalation through service disruption and resource consumption attacks. Organizations using ICU libraries in their applications should prioritize immediate remediation through version updates to ICU 60.2 or later, which contain the necessary patches to address this buffer overflow condition. Additionally, implementing proper input validation and sanitization at application layers can provide additional defense-in-depth measures, though the primary mitigation remains the library update to eliminate the root cause of the vulnerability.