CVE-2018-8778 in macOS
Summary
by MITRE
In Ruby before 2.2.10, 2.3.x before 2.3.7, 2.4.x before 2.4.4, 2.5.x before 2.5.1, and 2.6.0-preview1, an attacker controlling the unpacking format (similar to format string vulnerabilities) can trigger a buffer under-read in the String#unpack method, resulting in a massive and controlled information disclosure.
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Analysis
by VulDB Data Team • 05/10/2026
The vulnerability identified as CVE-2018-8778 represents a critical buffer under-read flaw in Ruby's String#unpack method that affects multiple versions of the Ruby programming language. This vulnerability arises from improper handling of unpacking format strings, creating a scenario where an attacker can manipulate the format specification to read data from memory locations that should remain protected. The flaw specifically impacts Ruby versions prior to 2.2.10, 2.3.7, 2.4.4, 2.5.1, and 2.6.0-preview1, making it a widespread issue affecting a significant portion of Ruby installations in production environments. The vulnerability is classified under CWE-126 as a buffer underrun condition, which falls within the broader category of memory safety issues that can lead to information disclosure and potential exploitation.
The technical implementation of this vulnerability stems from the String#unpack method's failure to properly validate or bounds-check the format string parameters provided by users. When Ruby processes unpacking operations, it expects specific format specifiers that define how binary data should be interpreted and extracted from strings. However, in affected versions, when an attacker supplies a malicious format string, the unpack method does not adequately verify that the format specification does not reference memory locations beyond the intended buffer boundaries. This allows the method to read data from adjacent memory locations, potentially exposing sensitive information such as stack contents, heap data, or other internal program state that should remain confidential. The controlled nature of this information disclosure means that an attacker can precisely determine which memory locations to read by crafting specific format strings, making this vulnerability particularly dangerous.
The operational impact of CVE-2018-8778 extends beyond simple information disclosure, as it can provide attackers with valuable insights into the memory layout of Ruby processes and potentially reveal sensitive data such as cryptographic keys, session tokens, or other confidential information stored in memory. This vulnerability is particularly concerning in web applications and server environments where Ruby applications process user input through unpack operations, as it can be exploited through various attack vectors including HTTP request parameters, file uploads, or any input that gets processed through String#unpack. The vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as attackers can leverage this flaw to gather intelligence before launching more sophisticated attacks, and it also maps to T1068 for Exploitation for Privilege Escalation when combined with other vulnerabilities in the attack chain. Applications using Ruby's unpack functionality in security-sensitive contexts face significant risk, as this vulnerability can be exploited to bypass security controls and potentially lead to full system compromise.
Organizations affected by this vulnerability should immediately upgrade to patched versions of Ruby to mitigate the risk of information disclosure and potential exploitation. The recommended mitigation strategy involves implementing comprehensive version management policies that ensure all Ruby installations are updated to versions 2.2.10, 2.3.7, 2.4.4, 2.5.1, or later releases where the vulnerability has been addressed. Additionally, developers should conduct thorough code reviews to identify any instances where String#unpack is used with user-controlled input, implementing proper input validation and sanitization measures before processing any format strings. Security monitoring should be enhanced to detect unusual patterns in unpack operations that might indicate exploitation attempts, and application firewalls or web application firewalls should be configured to filter potentially malicious format strings before they reach the Ruby interpreter. The vulnerability demonstrates the importance of rigorous input validation in interpreted languages and highlights the need for regular security assessments of all dependencies in application environments.