CVE-2019-9192 in C Library
Summary
by MITRE
** DISPUTED ** In the GNU C Library (aka glibc or libc6) through 2.29, check_dst_limits_calc_pos_1 in posix/regexec.c has Uncontrolled Recursion, as demonstrated by '(|)(\\1\\1)*' in grep, a different issue than CVE-2018-20796. NOTE: the software maintainer disputes that this is a vulnerability because the behavior occurs only with a crafted pattern.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2019-9192 pertains to the GNU C Library (glibc) version 2.29 and earlier, specifically within the posix/regexec.c file where the check_dst_limits_calc_pos_1 function exhibits uncontrolled recursion behavior. This issue manifests when processing regular expressions containing crafted patterns such as '(|)(\1\1)*' in grep utility, representing a distinct problem from CVE-2018-20796 which addresses different recursive behavior patterns. The technical flaw resides in how the regular expression engine handles certain backreference patterns that cause exponential backtracking and recursive function calls without proper termination conditions, creating a potential denial of service scenario.
The operational impact of this vulnerability stems from the fact that when maliciously crafted regular expressions are processed by applications relying on glibc's regex implementation, the system may experience significant performance degradation or complete system hang due to the unbounded recursion. This affects numerous Unix-like systems and applications that utilize standard POSIX regular expression functions, including grep, sed, and various system utilities. The vulnerability demonstrates a classic example of exponential time complexity in regular expression matching where the number of possible execution paths grows exponentially with input size, leading to resource exhaustion.
From a cybersecurity perspective, this vulnerability aligns with CWE-674 Uncontrolled Recursion, which describes situations where recursive calls lack proper termination conditions or bounds checking. The behavior also maps to ATT&CK technique T1496 Resource Exhaustion, as it can cause systems to consume excessive computational resources. The software maintainers have disputed the vulnerability classification, arguing that the behavior only occurs with crafted patterns that would not typically appear in normal usage scenarios, however security researchers maintain that such patterns could be exploited in contexts where regular expressions are processed with untrusted input. The disputed nature of this vulnerability highlights the ongoing debate between false positive reporting and legitimate security concerns in the broader security community.
Mitigation strategies for CVE-2019-9192 involve upgrading to glibc version 2.30 or later where the issue has been addressed through improved bounds checking and recursion limiting mechanisms. System administrators should also implement input validation and sanitization measures for any applications that process regular expressions from untrusted sources. Additionally, implementing resource limits and timeouts on regex processing operations can help prevent exploitation attempts. Organizations should conduct vulnerability assessments to identify applications that may be susceptible to this type of recursive denial of service attack and ensure proper patch management protocols are in place to maintain system security posture.