CVE-2016-8859 in TRE Library
Summary
by MITRE
Multiple integer overflows in the TRE library and musl libc allow attackers to cause memory corruption via a large number of (1) states or (2) tags, which triggers an out-of-bounds write.
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Analysis
by VulDB Data Team • 11/14/2022
The vulnerability identified as CVE-2016-8859 represents a critical security flaw affecting the TRE regular expression library and musl libc implementations. This issue stems from improper handling of integer overflow conditions during the processing of regular expressions containing excessive states or tags. The vulnerability manifests when applications using these libraries encounter regular expressions with a large number of states or tags, leading to arithmetic overflow conditions that ultimately result in memory corruption and potential out-of-bounds write operations. The flaw exists in the core parsing and compilation logic of these libraries, where integer variables representing state counts or tag indices are not properly validated against their maximum representable values before being used in memory allocation calculations or array indexing operations.
The technical execution of this vulnerability involves attackers crafting malicious regular expressions containing an excessive number of states or tags that, when processed by affected libraries, trigger integer overflow conditions. When the integer variables exceed their maximum values, they wrap around to negative or unexpectedly large values, causing subsequent memory allocation calculations to allocate insufficient memory or array indexing operations to access memory locations outside the intended boundaries. This integer overflow behavior falls under the common weakness identified as CWE-190, which specifically addresses integer overflow conditions that can lead to memory corruption. The vulnerability is particularly dangerous because it allows attackers to manipulate memory layout and potentially execute arbitrary code through controlled memory corruption, making it a prime target for exploitation in privilege escalation scenarios or remote code execution attacks.
The operational impact of CVE-2016-8859 extends across numerous systems and applications that rely on TRE library or musl libc for regular expression processing. This includes web servers, network appliances, embedded systems, and any software that performs regular expression matching on untrusted input. The vulnerability can be exploited in various attack scenarios including buffer overflow exploitation, heap corruption, and potential privilege escalation when applications running with elevated privileges process malicious regular expressions. The attack surface is broad since many applications use regular expressions for input validation, log parsing, and pattern matching operations, making the exploitation potential widespread across different software domains. According to ATT&CK framework category T1059, this vulnerability enables adversary techniques involving command and scripting interpreter execution through malformed input processing.
Mitigation strategies for CVE-2016-8859 require immediate attention from system administrators and software maintainers. The primary recommendation involves updating to patched versions of both the TRE library and musl libc implementations, as vendors have released security updates addressing the integer overflow conditions. Additionally, implementing input validation and sanitization measures can help reduce the risk of exploitation by limiting the complexity of regular expressions processed by affected applications. Deploying memory protection mechanisms such as stack canaries, address space layout randomization, and data execution prevention can provide additional defense-in-depth layers. Organizations should also implement monitoring and logging of regular expression processing activities to detect potential exploitation attempts and establish proper resource limits on regular expression complexity to prevent denial-of-service conditions. The vulnerability demonstrates the critical importance of proper integer overflow handling in security-critical libraries and reinforces the necessity of thorough input validation and bounds checking in system components that process user-supplied data.