CVE-2021-28092 in is-svg Package
Summary
by MITRE • 03/13/2021
The is-svg package 2.1.0 through 4.2.1 for Node.js uses a regular expression that is vulnerable to Regular Expression Denial of Service (ReDoS). If an attacker provides a malicious string, is-svg will get stuck processing the input for a very long time.
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Analysis
by VulDB Data Team • 04/01/2021
The CVE-2021-28092 vulnerability resides within the is-svg package version range 2.1.0 through 4.2.1 for Node.js environments, representing a critical security flaw that exposes applications to Regular Expression Denial of Service (ReDoS) attacks. This vulnerability stems from the package's implementation of regular expressions that are susceptible to catastrophic backtracking, a well-documented weakness in regex pattern matching that allows attackers to craft input strings designed to cause exponential execution time increases. The affected package is commonly used in web applications and server-side environments to validate whether provided input represents valid svg markup, making it a prime target for malicious exploitation. The vulnerability operates by leveraging specific character sequences that trigger the regex engine to perform an enormous number of backtracking operations, effectively consuming system resources and causing the application to become unresponsive or crash entirely.
The technical flaw manifests in the regular expression patterns used within the is-svg package's validation logic, where the regex engine encounters input strings that cause it to explore an exponentially growing number of possible matching paths. This behavior directly aligns with CWE-400, which categorizes the vulnerability as a Regular Expression Denial of Service attack, and represents a classic example of how seemingly innocuous input validation can become a vector for system compromise. When an attacker supplies a specially crafted malicious string to the package's validation function, the regular expression engine enters a state where it repeatedly backtracks through the same input positions, leading to computational overhead that can escalate to minutes or even hours of processing time for relatively short input strings. The vulnerability demonstrates how the ATT&CK framework's technique T1496 for Resource Exhaustion can be effectively implemented through the manipulation of regular expression patterns within common Node.js libraries.
The operational impact of CVE-2021-28092 extends beyond simple performance degradation to potentially enable complete system compromise through service disruption. Applications utilizing vulnerable versions of the is-svg package become susceptible to denial of service attacks that can render them unavailable to legitimate users, particularly in high-traffic environments where input validation occurs frequently. The vulnerability affects any Node.js application that processes user-provided input through the is-svg validation function, including web applications, API endpoints, and server-side rendering systems. Attackers can exploit this vulnerability by simply submitting malicious input to endpoints that utilize the package, causing the application to hang or consume excessive CPU resources. This type of vulnerability is particularly dangerous in cloud environments or containerized applications where resource limits may be enforced, as the excessive resource consumption can trigger automatic scaling mechanisms or cause application crashes that impact service availability. Organizations using vulnerable versions of the package should consider the potential for cascading failures, as the denial of service can propagate through dependent systems and services that rely on the affected package for input validation.
Mitigation strategies for CVE-2021-28092 primarily involve updating to a patched version of the is-svg package, which typically includes the implementation of more robust and optimized regular expressions that prevent catastrophic backtracking. Security teams should conduct comprehensive inventory audits to identify all applications and systems utilizing vulnerable package versions, particularly focusing on Node.js environments that process external input through svg validation functions. The remediation process should include immediate patching of affected systems, followed by thorough testing to ensure that the updated package maintains expected functionality without introducing regressions. Additional defensive measures include implementing input validation at multiple layers of the application architecture, using rate limiting and request timeouts to prevent exploitation attempts, and monitoring for unusual processing patterns that may indicate ReDoS attacks. Organizations should also consider implementing regular security scanning of their dependency trees to identify and remediate similar vulnerabilities in other third-party packages, as the ReDoS attack vector is prevalent across many commonly used libraries and frameworks in the Node.js ecosystem.