CVE-2017-9227 in Oniguruma
Summary
by MITRE
An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds read occurs in mbc_enc_len() during regular expression searching. Invalid handling of reg->dmin in forward_search_range() could result in an invalid pointer dereference, as an out-of-bounds read from a stack buffer.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9227 represents a critical stack out-of-bounds read condition affecting regular expression processing libraries in multiple programming environments. This flaw manifests within the Oniguruma regular expression engine version 6.2.0, which serves as the foundation for text processing capabilities in Ruby through version 2.4.1 and PHP through version 7.1.5. The vulnerability stems from improper memory management during pattern matching operations, specifically within the mbc_enc_len() function that handles multi-byte character encoding length calculations. The issue occurs when the regular expression engine processes certain malformed input patterns, leading to memory access violations that can potentially be exploited by malicious actors.
The technical implementation of this vulnerability involves a critical flaw in the forward_search_range() function where reg->dmin is improperly handled, creating a scenario where an invalid pointer dereference occurs during regular expression evaluation. This improper handling results in an out-of-bounds read from a stack buffer, allowing attackers to potentially access memory locations beyond the intended buffer boundaries. The vulnerability is classified under CWE-125 as an out-of-bounds read, which falls within the broader category of memory safety issues that have historically led to numerous exploitable conditions. The flaw specifically impacts the stack-based memory allocation patterns used by the regular expression engine during pattern matching operations, making it particularly dangerous in environments where untrusted input is processed through regular expression functions.
The operational impact of CVE-2017-9227 extends across multiple software ecosystems, affecting web applications, scripting environments, and text processing systems that rely on regular expression capabilities. When exploited, this vulnerability can lead to application crashes, denial of service conditions, or potentially more severe consequences including arbitrary code execution depending on the specific implementation and memory layout. The vulnerability is particularly concerning in web applications where user input is processed through regular expression functions, as attackers can craft malicious patterns that trigger the out-of-bounds read condition. This type of vulnerability aligns with ATT&CK technique T1059.007 for scripting and T1555.001 for credentials from password storage, as it can be leveraged to compromise systems through memory corruption attacks. The vulnerability affects both Ruby applications using the oniguruma-mod library and PHP applications utilizing the mbstring extension, creating a wide attack surface across different development environments.
Mitigation strategies for CVE-2017-9227 require immediate patching of affected software components to address the underlying memory handling issues in the Oniguruma regular expression engine. System administrators should prioritize updating Ruby installations to versions 2.4.2 or later and PHP installations to versions 7.1.6 or later, which contain the necessary fixes for this vulnerability. Additionally, implementing proper input validation and sanitization practices can help reduce the attack surface by limiting the exposure to malformed regular expression patterns. Organizations should also consider implementing runtime protections such as stack canaries, address space layout randomization, and heap metadata protection to make exploitation more difficult. Monitoring and logging of regular expression processing activities can help detect potential exploitation attempts, while regular security assessments of applications using these libraries can identify additional vulnerabilities that may compound the risk of this particular flaw. The vulnerability demonstrates the importance of proper memory management in text processing libraries and highlights the need for comprehensive testing of edge cases in regular expression engines.