CVE-2017-9225 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 write in onigenc_unicode_get_case_fold_codes_by_str() occurs during regular expression compilation. Code point 0xFFFFFFFF is not properly handled in unicode_unfold_key(). A malformed regular expression could result in 4 bytes being written off the end of a stack buffer of expand_case_fold_string() during the call to onigenc_unicode_get_case_fold_codes_by_str(), a typical stack buffer overflow.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability described in CVE-2017-9225 represents a critical stack buffer overflow issue affecting regular expression processing libraries used in multiple programming environments including Ruby and PHP. This flaw exists within the Oniguruma regular expression engine version 6.2.0, which serves as the underlying component for text processing in these languages. The vulnerability manifests during the compilation phase of regular expressions when the system attempts to handle Unicode case folding operations, specifically when processing code point 0xFFFFFFFF which is not properly validated or handled within the unicode_unfold_key() function.
The technical implementation of this vulnerability stems from inadequate bounds checking in the expand_case_fold_string() function during regular expression compilation. When a malformed regular expression containing the specific Unicode code point 0xFFFFFFFF is processed, the onigenc_unicode_get_case_fold_codes_by_str() function executes a stack-based buffer overflow operation. This occurs because the system attempts to write 4 bytes of data beyond the allocated stack buffer boundaries, creating a condition where arbitrary memory locations can be overwritten with attacker-controlled data. The flaw is particularly dangerous because it operates during the compilation phase rather than execution, meaning that simply processing a malicious regular expression string can trigger the overflow condition.
The operational impact of this vulnerability extends across multiple software ecosystems where Oniguruma is integrated, specifically affecting Ruby versions through 2.4.1 and PHP versions through 7.1.5. Attackers can leverage this vulnerability through crafted regular expressions that, when processed by applications using these affected versions, can lead to remote code execution, application crashes, or system instability. The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions. From an attack framework perspective, this vulnerability maps to ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation could allow adversaries to execute arbitrary code on vulnerable systems.
Mitigation strategies for CVE-2017-9225 require immediate patching of affected software components to upgrade to versions containing fixed implementations of the Oniguruma library. System administrators should prioritize updating Ruby and PHP installations to versions that incorporate patched regular expression engines. Additionally, input validation measures should be implemented to sanitize regular expression inputs, particularly when processing user-supplied data. The vulnerability demonstrates the importance of robust bounds checking in Unicode processing functions and highlights the need for comprehensive testing of internationalization features. Organizations should also consider implementing application-level restrictions on regular expression complexity and length to reduce the attack surface, while monitoring for unusual patterns in regex processing that might indicate exploitation attempts.