CVE-2017-5357 in GNU
Summary
by MITRE
regex.c in GNU ed before 1.14.1 allows attackers to cause a denial of service (crash) via a malformed command, which triggers an invalid free.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2017-5357 resides within the GNU ed text editor's regular expression processing component, specifically in the regex.c file. This issue affects GNU ed versions prior to 1.14.1 and represents a critical security flaw that can be exploited to trigger a denial of service condition through carefully crafted malformed commands. The vulnerability stems from improper handling of memory management during regular expression evaluation, where the software attempts to free memory that has already been freed or is otherwise invalid, leading to a crash of the application. This type of vulnerability falls under the category of memory corruption issues that can severely impact system availability and stability.
The technical exploitation of this vulnerability occurs when an attacker submits a malformed command to the GNU ed text editor that contains malformed regular expressions. During processing, the regex.c component fails to properly validate memory references, causing the application to attempt an invalid free operation on memory that has either already been deallocated or is not properly allocated for freeing. This invalid memory operation results in a segmentation fault or similar memory access violation that terminates the ed process. The flaw demonstrates characteristics consistent with CWE-415: Double Free, where the same memory block is freed twice, or CWE-416: Use After Free, where memory is accessed after it has been freed. The vulnerability is particularly concerning because it can be triggered through normal command-line interaction with the text editor, making it accessible to any user who can invoke ed with malicious input.
From an operational standpoint, this vulnerability presents significant risks to systems where GNU ed is installed and actively used, particularly in environments where the editor is available to untrusted users or when it's part of automated processing pipelines. The denial of service impact can be substantial as it renders the text editor completely unusable until the process is manually restarted or the system is rebooted. In server environments or automated systems, this could lead to service disruption and potentially allow for more sophisticated attacks if the vulnerability is combined with other exploitation techniques. The vulnerability also represents a potential vector for privilege escalation in scenarios where ed is used with elevated privileges or in restricted environments where users might have limited access to other system tools. According to ATT&CK framework, this vulnerability aligns with T1499.004: Endpoint Denial of Service, where adversaries may target applications to disrupt their availability.
Mitigation strategies for CVE-2017-5357 primarily focus on immediate patching of affected GNU ed installations to version 1.14.1 or later, which contains the necessary fixes for proper memory management in the regex.c component. System administrators should also implement input validation measures to prevent malformed commands from reaching the ed process, particularly in environments where untrusted input is processed. Additional protective measures include restricting access to the ed command where possible, implementing proper privilege separation, and monitoring for abnormal process termination patterns that might indicate exploitation attempts. Organizations should also consider implementing application whitelisting policies that limit execution of potentially vulnerable text editors in restricted environments. The vulnerability highlights the importance of regular security updates and proper code review processes for memory management operations, particularly in widely deployed system utilities where the impact of denial of service attacks can be significant across multiple user environments.