CVE-2017-8911 in tnef
Summary
by MITRE
An integer underflow has been identified in the unicode_to_utf8() function in tnef 1.4.14. This might lead to invalid write operations, controlled by an attacker.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability CVE-2017-8911 represents a critical integer underflow condition within the unicode_to_utf8() function of the tnef library version 1.4.14. This flaw occurs during the conversion process from unicode to utf-8 encoding where an attacker can manipulate input data to cause arithmetic underflow conditions. The tnef library is commonly used for processing transport neutral encoding format files, which are often encountered in email systems and document processing applications. When the integer underflow occurs, it can result in memory corruption that manifests as invalid write operations at unpredictable memory locations. This type of vulnerability falls under the CWE-191 integer underflow category, which is classified as a weakness that can lead to memory corruption and potentially arbitrary code execution. The vulnerability is particularly concerning because it allows attackers to control the memory write operations through crafted input data, making it a prime target for exploitation in buffer overflow scenarios.
The operational impact of this vulnerability extends across multiple domains where tnef processing is implemented, including email servers, document management systems, and file processing applications. When an attacker successfully exploits this integer underflow, they can manipulate the program flow by writing to memory locations that should remain protected or unmodified. This condition can lead to denial of service attacks where applications crash due to memory corruption, or more severe exploitation scenarios where attackers achieve privilege escalation or arbitrary code execution. The vulnerability is particularly dangerous in email processing environments where tnef files are commonly embedded in emails, as attackers can craft malicious email attachments that trigger this condition when processed by vulnerable applications. The ATT&CK framework categorizes this type of vulnerability under the T1059.007 technique for command and scripting interpreter, as exploitation often involves crafting specific payloads that can be executed within the target environment.
Mitigation strategies for CVE-2017-8911 should focus on immediate patching of the tnef library to version 1.4.15 or later, which contains the necessary fixes for the integer underflow condition. Organizations should implement input validation measures to sanitize all unicode data before processing, particularly when dealing with external or untrusted sources. Memory protection mechanisms such as stack canaries, address space layout randomization, and data execution prevention should be enabled to reduce the effectiveness of exploitation attempts. Additionally, network segmentation and access controls can limit the potential impact of successful exploitation by restricting access to vulnerable systems. Security monitoring should include detection of unusual memory access patterns and process behavior that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper integer overflow and underflow checking in cryptographic and encoding functions, as these operations are fundamental to data processing and conversion tasks. Organizations should also consider implementing automated vulnerability scanning tools that can detect the presence of vulnerable library versions and provide alerts for necessary updates. Regular security assessments of third-party libraries and dependencies are essential to prevent similar vulnerabilities from being introduced into production environments through supply chain attacks or outdated components.