CVE-2021-27290 in GraalVM Enterprise Edition
Summary
by MITRE • 03/13/2021
ssri 5.2.2-8.0.0, fixed in 8.0.1, processes SRIs using a regular expression which is vulnerable to a denial of service. Malicious SRIs could take an extremely long time to process, leading to denial of service. This issue only affects consumers using the strict option.
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Analysis
by VulDB Data Team • 10/25/2021
The vulnerability identified as CVE-2021-27290 affects the ssri package version range 5.2.2 through 8.0.0, specifically targeting the regular expression processing mechanism used for Subresource Integrity (SRI) validation. This issue represents a classic denial of service vulnerability where malicious input causes unexpectedly long processing times, ultimately leading to system resource exhaustion and service unavailability. The vulnerability is particularly concerning because it affects the strict mode processing within the ssri library, which is commonly used in package managers and dependency resolution systems to validate integrity hashes of downloaded resources.
The technical flaw stems from the implementation of regular expressions used to parse and validate SRI values, which are designed to verify the integrity of web resources by checking their cryptographic hashes against expected values. When processing maliciously crafted SRI strings, the regular expression engine enters into a computationally expensive backtracking state, causing exponential time complexity during pattern matching operations. This behavior is characteristic of regular expression denial of service vulnerabilities where poorly constructed patterns can be exploited to cause significant performance degradation. The vulnerability maps directly to CWE-400, which classifies uncontrolled resource consumption as a weakness that can lead to denial of service conditions.
The operational impact of this vulnerability extends beyond simple service disruption as it affects systems that rely on strict SRI validation for security purposes. Package managers, build systems, and dependency resolution tools that utilize ssri in strict mode become susceptible to attacks where adversaries can craft malicious SRI strings to cause processing delays or complete system hangs. This vulnerability particularly affects environments where automated dependency resolution occurs, as a single malicious package could potentially bring down entire build pipelines or package management systems. The attack surface is broad since ssri is a widely used library in npm ecosystems and other package management systems that implement SRI validation.
Mitigation strategies for CVE-2021-27290 require immediate patching to version 8.0.1 or later where the regular expression processing has been corrected to prevent backtracking attacks. Organizations should also implement input validation and rate limiting mechanisms to prevent malicious SRI strings from being processed in the first place. Additionally, security monitoring should be enhanced to detect unusual processing times or resource consumption patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper regular expression design and the need for security testing of parsing logic, particularly in libraries that handle untrusted input. This issue aligns with ATT&CK technique T1496 which covers resource exhaustion attacks, and highlights the necessity of implementing proper input sanitization and validation in security-critical components of software supply chains.