CVE-2021-46345 in JerryScript
Summary
by MITRE • 01/21/2022
There is an Assertion 'cesu8_cursor_p == cesu8_end_p' failed at /jerry-core/lit/lit-strings.c in JerryScript 3.0.0.
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Analysis
by VulDB Data Team • 01/26/2022
The vulnerability identified as CVE-2021-46345 represents a critical assertion failure within the JerryScript JavaScript engine version 3.0.0, specifically located in the literal string processing component at /jerry-core/lit/lit-strings.c. This assertion failure occurs during the processing of CESU-8 encoded strings, where the engine expects a cursor pointer to reach the end of the CESU-8 string data but encounters a mismatch between the expected and actual cursor positions. The issue stems from improper handling of string encoding boundaries, particularly when processing certain sequences of characters that fall outside the standard utf-8 range but are valid within CESU-8 encoding standards. This type of assertion failure typically indicates that the engine's internal state management has encountered an unexpected condition that violates its assumptions about valid string processing flows. The vulnerability manifests as a potential denial of service condition or could potentially be exploited to cause unexpected program termination, making it particularly concerning for systems that rely on JerryScript for embedded JavaScript execution.
The technical flaw underlying CVE-2021-46345 resides in the string processing logic that handles CESU-8 encoding validation and cursor advancement. When JerryScript encounters a string containing CESU-8 encoded characters, the engine maintains internal cursor pointers to track progress through the byte stream. The assertion failure occurs because the engine's logic assumes that when processing a complete CESU-8 string, the cursor position should exactly match the end pointer of the string data. However, certain malformed or edge-case character sequences can cause the cursor to either advance beyond the expected boundary or fail to reach it, leading to the assertion failure. This represents a classic example of inadequate input validation and boundary checking within string processing routines, which aligns with CWE-617: Reachable Assertion, where an assertion can be triggered by malicious input. The flaw demonstrates poor error handling in the face of unexpected string encoding patterns, particularly in how the engine manages state transitions during string parsing operations.
The operational impact of CVE-2021-46345 extends beyond simple program termination, as it can severely affect the stability and reliability of systems that utilize JerryScript for JavaScript execution. In embedded environments or IoT devices where JerryScript is commonly deployed, this vulnerability could be exploited to cause persistent service disruptions or system crashes, potentially leading to denial of service conditions that compromise device availability. The vulnerability's exploitation potential increases when considering that JavaScript engines are often used in web browsers, embedded systems, and server-side applications where input validation is paramount. Security researchers have noted that such assertion failures in JavaScript engines can potentially be leveraged for more sophisticated attacks, including information disclosure or privilege escalation depending on the execution context. The vulnerability particularly affects systems where JerryScript is used to process untrusted input data, such as user-generated content, API responses, or configuration files that may contain malformed CESU-8 sequences.
Mitigation strategies for CVE-2021-46345 should prioritize immediate software updates to JerryScript versions that address the assertion failure in string processing logic. Organizations should implement comprehensive input validation measures to filter or sanitize any CESU-8 encoded data before processing, particularly in applications that accept external input. The fix typically involves strengthening boundary checking in the string parsing routines to ensure that cursor advancement logic properly accounts for all valid CESU-8 encoding patterns and edge cases. Security teams should also consider implementing runtime monitoring to detect assertion failures or abnormal program termination patterns that may indicate exploitation attempts. Additionally, deploying defensive programming practices such as input sanitization, bounded string operations, and comprehensive error handling can reduce the attack surface for similar vulnerabilities. The remediation process should include thorough regression testing to ensure that the fix does not introduce new behavioral changes or performance regressions in legitimate string processing operations. Organizations should also review their deployment configurations to ensure that JerryScript is not exposed to untrusted input sources without proper sanitization layers, aligning with ATT&CK technique T1203: Exploitation for Client Execution where vulnerabilities are leveraged to execute malicious code through application interfaces.