CVE-2020-23308 in JerryScript
Summary
by MITRE • 06/11/2021
There is an Assertion 'context_p->stack_top_uint8 == LEXER_EXPRESSION_START' at js-parser-expr.c:3565 in parser_parse_expression in JerryScript 2.2.0.
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Analysis
by VulDB Data Team • 06/13/2021
This vulnerability exists in JerryScript version 2.2.0 within the JavaScript parser component at line 3565 in the js-parser-expr.c file. The issue manifests as an assertion failure occurring when the parser attempts to process certain JavaScript expressions, specifically when the context stack top value does not match the expected LEXER_EXPRESSION_START constant. This assertion mechanism is designed to catch programming errors during development but becomes problematic when triggered in production environments.
The technical flaw stems from improper state management within the JavaScript expression parser where the parser's internal stack tracking mechanism fails to maintain consistent state during expression parsing operations. When the parser encounters specific syntactic constructs or malformed input sequences, it attempts to verify that the current stack position aligns with the expected expression start state, but this verification fails, causing the assertion to trigger and potentially leading to application termination or unexpected behavior.
The operational impact of this vulnerability extends beyond simple assertion failures as it represents a potential denial of service condition that could be exploited by malicious actors. An attacker could craft specific JavaScript code sequences that would trigger this assertion failure, causing the JavaScript engine to crash or behave unpredictably. This vulnerability affects any application or system that relies on JerryScript for JavaScript execution, particularly those using it in embedded environments or IoT devices where such crashes could have significant operational consequences.
From a cybersecurity perspective, this vulnerability aligns with CWE-611 Improper Restriction of XML External Entity Reference and CWE-248 Uncaught Exception, as it represents an unhandled state condition that could lead to system instability. The issue also connects to ATT&CK technique T1203 Exploitation for Client Execution where adversaries might leverage such parser vulnerabilities to disrupt services or potentially escalate privileges. The vulnerability demonstrates poor input validation and state management within the parser component, making it susceptible to exploitation through carefully crafted JavaScript input that triggers the assertion failure condition.
The recommended mitigation strategy involves upgrading to a patched version of JerryScript where this assertion has been properly handled or removed. Organizations should also implement input validation measures to prevent malformed JavaScript from reaching the parser component, though this may not fully address the underlying issue. Additionally, deploying application-level sandboxing and monitoring mechanisms can help detect and respond to such assertion failures before they can cause significant disruption to services relying on JerryScript for JavaScript execution.