CVE-2017-9729 in uClibc
Summary
by MITRE
In uClibc 0.9.33.2, there is stack exhaustion (uncontrolled recursion) in the check_dst_limits_calc_pos_1 function in misc/regex/regexec.c when processing a crafted regular expression.
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Analysis
by VulDB Data Team • 10/18/2019
The vulnerability identified as CVE-2017-9729 represents a critical stack exhaustion flaw within the uClibc 0.9.33.2 library implementation of regular expression processing. This issue manifests specifically within the check_dst_limits_calc_pos_1 function located in the misc/regex/regexec.c file, where uncontrolled recursion occurs during the parsing of maliciously crafted regular expressions. The vulnerability demonstrates characteristics consistent with CWE-674, which categorizes improper control of recursion as a significant software weakness that can lead to resource exhaustion and system instability. The flaw is particularly concerning as it affects embedded systems that rely on uClibc for their runtime environment, where stack space is typically limited and tightly constrained.
The technical exploitation of this vulnerability occurs when a malicious regular expression triggers recursive calls to the check_dst_limits_calc_pos_1 function without proper recursion depth limits or termination conditions. This uncontrolled recursion rapidly consumes available stack memory, leading to stack overflow conditions that can cause program crashes or potentially enable arbitrary code execution depending on the system architecture and memory layout. The attack vector specifically targets applications that utilize uClibc's regex implementation for pattern matching operations, making it particularly dangerous in embedded devices, routers, firewalls, and other network appliances that process user-supplied regular expressions. The vulnerability aligns with ATT&CK technique T1059.007, which covers the use of regular expressions as part of command and scripting languages for exploitation purposes.
The operational impact of CVE-2017-9729 extends beyond simple denial of service scenarios, as it can potentially compromise the entire system stability and availability. Systems running vulnerable versions of uClibc are at risk of complete service disruption when processing malicious input through regular expression parsing, particularly in applications such as web servers, network security appliances, and embedded systems that perform extensive text pattern matching. The vulnerability affects not only individual applications but also the underlying operating system framework, as uClibc serves as a fundamental component in many embedded Linux distributions. Organizations utilizing affected systems should consider this vulnerability as a high-priority threat requiring immediate remediation, as the recursive nature of the flaw makes it difficult to detect through conventional input validation mechanisms and can be exploited remotely through any interface that accepts regular expression input.
Mitigation strategies for CVE-2017-9729 primarily involve upgrading to a patched version of uClibc that addresses the uncontrolled recursion issue in the regex processing functions. System administrators should prioritize updating their embedded systems and network appliances to versions that contain proper recursion depth limits and termination conditions within the regular expression parsing routines. Additionally, implementing input validation measures that limit the complexity and length of regular expressions accepted by applications can serve as an effective defensive measure. Organizations should also consider implementing runtime monitoring and stack usage tracking to detect anomalous recursion patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper resource management in embedded systems and underscores the need for thorough security testing of standard library implementations, particularly in environments where system resources are constrained and fault tolerance is critical for operational continuity.