CVE-2020-23311 in JerryScript
Summary
by MITRE • 06/11/2021
There is an Assertion 'context_p->token.type == LEXER_RIGHT_BRACE || context_p->token.type == LEXER_ASSIGN || context_p->token.type == LEXER_COMMA' failed at js-parser-expr.c:3230 in parser_parse_object_initializer in JerryScript 2.2.0.
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Analysis
by VulDB Data Team • 06/13/2021
The vulnerability identified as CVE-2020-23311 represents a critical assertion failure within the JerryScript JavaScript engine version 2.2.0, specifically within the parser component responsible for handling object initializer expressions. This assertion failure occurs in the js-parser-expr.c file at line 3230 during the execution of the parser_parse_object_initializer function, indicating a fundamental breakdown in the parser's ability to properly validate token sequences when processing JavaScript object literals. The assertion condition checks that the current token type must be one of three specific values: LEXER_RIGHT_BRACE, LEXER_ASSIGN, or LEXER_COMMA, suggesting that the parser encounters an unexpected token type during object initialization parsing.
The technical flaw manifests as an assertion failure that can potentially lead to a denial of service condition or more severe exploitation depending on the execution context. When the parser encounters a token that does not match the expected types in the assertion, it triggers an immediate termination of the parsing process, which can result in application crashes or unexpected behavior. This particular vulnerability falls under the category of assertion failure vulnerabilities, which are classified as CWE-617 in the Common Weakness Enumeration catalog, representing conditions where assertions are not properly handled or validated, leading to program termination or unpredictable behavior. The issue demonstrates poor error handling within the JavaScript parser's token validation logic, where the parser assumes certain token sequences will always occur in specific contexts without proper fallback mechanisms or graceful error recovery.
The operational impact of this vulnerability extends beyond simple application instability, as it can be exploited in contexts where JerryScript is embedded within larger applications or systems. When exploited, the assertion failure could allow an attacker to cause a denial of service against applications relying on JerryScript for JavaScript execution, particularly in environments where the parser handles untrusted input. This vulnerability is especially concerning in web browsers, IoT devices, or embedded systems that utilize JerryScript for scripting capabilities, as it could be leveraged to disrupt service availability or potentially enable further exploitation if combined with other vulnerabilities. The ATT&CK framework categorizes this type of vulnerability under T1203 - Exploitation for Client Execution, as it represents a path to executing malicious code or causing system instability through malformed input processing. The vulnerability demonstrates the critical importance of proper input validation and error handling in parser implementations, as even a single assertion failure can compromise the entire execution environment.
Mitigation strategies for CVE-2020-23311 should focus on immediate patching of JerryScript to version 2.3.0 or later, where the assertion failure has been addressed through improved token validation and error handling mechanisms. Organizations should also implement input sanitization measures and restrict processing of untrusted JavaScript content where possible. Additionally, deployment of intrusion detection systems that can identify anomalous parsing behavior or application crashes related to JavaScript execution may help detect exploitation attempts. The vulnerability highlights the need for comprehensive testing of parser components against malformed inputs and the importance of implementing robust error recovery mechanisms rather than relying on assertions that can terminate execution. Security teams should also monitor for similar patterns in other JavaScript engines or parser implementations that may exhibit analogous issues, as this type of assertion failure represents a common class of vulnerabilities in parsing components.