CVE-2018-7651 in ssri Module
Summary
by MITRE
index.js in the ssri module before 5.2.2 for Node.js is prone to a regular expression denial of service vulnerability in strict mode functionality via a long base64 hash string.
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Analysis
by VulDB Data Team • 02/16/2023
The ssri module version 5.2.1 and earlier in Node.js contains a regular expression denial of service vulnerability that affects the strict mode functionality. This vulnerability stems from the index.js file's handling of base64 hash strings during strict mode validation processes. The flaw occurs when the module processes excessively long base64 encoded strings, causing the regular expression engine to enter into a catastrophic backtracking state that consumes excessive computational resources. The vulnerability specifically manifests when the module attempts to validate content integrity using strict mode enforcement, which is commonly employed in package management and security verification contexts. This issue represents a classic reDoS (Regular Expression Denial of Service) attack vector where malicious input can cause significant performance degradation or complete system unresponsiveness.
The technical implementation of this vulnerability involves the regular expression patterns used within the strict mode validation logic of the ssri module. When processing base64 hash strings that exceed normal length parameters, these patterns exhibit exponential backtracking behavior, where the regex engine must explore an exponentially growing number of possible matching paths. This backtracking occurs due to overlapping quantifiers and alternation patterns in the regular expressions that are designed to validate the structure of base64 encoded content. The vulnerability is particularly dangerous because it can be triggered through legitimate package management workflows where dependency resolution and integrity checking processes might encounter malformed or maliciously crafted base64 strings. This issue falls under CWE-400 which specifically addresses uncontrolled resource consumption, and more precisely aligns with CWE-1333 which covers regular expression vulnerabilities.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially enable denial of service attacks against Node.js applications that utilize the ssri module for content integrity verification. Attackers can exploit this weakness by providing carefully crafted long base64 hash strings that trigger the vulnerable regular expression patterns, causing the application to consume excessive CPU cycles and memory resources. This vulnerability affects various Node.js package management tools and dependency resolution systems that rely on ssri for validating package integrity, potentially compromising the availability of critical services. The impact is particularly severe in environments where automated package installation and update processes are frequent, as these scenarios provide multiple opportunities for exploitation. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers network denial of service attacks, and T1595.001 which covers network scanning techniques that could be used to identify vulnerable systems.
Mitigation strategies for this vulnerability include immediate upgrading to ssri version 5.2.2 or later, which contains the patched regular expression patterns that prevent catastrophic backtracking. Organizations should also implement input validation measures that limit the length of base64 strings processed by the module, particularly in environments where untrusted input might be processed. Additional defensive measures include monitoring for unusual resource consumption patterns that could indicate exploitation attempts, and implementing rate limiting on package installation and verification operations. System administrators should also consider implementing network segmentation and access controls to limit exposure of systems that process package dependencies. The fix implemented in the patched version addresses the core issue by replacing the vulnerable regular expressions with more efficient patterns that do not exhibit exponential backtracking behavior, thereby ensuring that even extremely long base64 strings can be processed without causing denial of service conditions.