CVE-2026-86315 in Escargot
Summary
by MITRE • 09/07/2026
An out-of-bounds write caused by numeric truncation Samsung Open Source Escargot on Linux x86-64 allows an attacker who can supply JavaScript for execution to corrupt native memory and crash the host process via a crafted class definition whose instance initialization entry count exceeds UINT16_MAX.
This issue affects Escargot: 5dc93606abd42b859045add05d704a038e197359.
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Analysis
by VulDB Data Team • 09/07/2026
The vulnerability identified in the Samsung Open Source Escargot JavaScript engine represents a critical memory safety flaw rooted in improper handling of numeric data types during class instantiation processes. Specifically, this issue manifests as an out-of-bounds write triggered by numeric truncation within the context of Linux x86-64 environments. The core technical failure occurs when processing crafted JavaScript code that defines classes with instance initialization entry counts exceeding the maximum value representable by a sixteen-bit unsigned integer (UINT16_MAX). Because the engine fails to validate or properly cast this count before using it as an array index or buffer size parameter, the large numeric value is truncated down to fit within the expected data type. This truncation results in a significantly smaller positive number being used for memory allocation and access operations, while the original logic assumes the larger magnitude was preserved. Consequently, when the engine attempts to write initialization data based on the untruncated expectation or misaligned pointers derived from this error, it writes beyond the allocated boundaries of native heap memory structures associated with the class instance.
From a technical perspective, this flaw aligns closely with CWE-190 Integer Overflow or Wraparound and CWE-787 Out-of-bounds Write. The truncation mechanism effectively bypasses standard bounds checking because the internal state believes it is operating within safe limits defined by the truncated value, while actual memory access patterns violate those boundaries due to the discrepancy between logical intent and physical execution. In modern JavaScript engines like Escargot, which are written in C++ for performance optimization, such low-level memory management errors can lead to severe consequences including heap corruption, arbitrary code execution if an attacker can control the overwritten data, or denial of service through segmentation faults that crash the host process hosting the engine. The specific trigger condition involving class definitions highlights a gap in validation logic during the compilation and instantiation phases where metadata regarding instance properties is processed.
The operational impact of this vulnerability is significant for any application relying on Escargot to execute untrusted JavaScript code, such as embedded web browsers, IoT device firmware interpreters, or server-side runtime environments that parse dynamic scripts. An attacker who can supply malicious JavaScript payloads to the engine can exploit this flaw to corrupt adjacent memory regions, potentially overwriting function pointers, object headers, or other critical control data structures within the native heap. This corruption typically leads to immediate process termination via a crash, resulting in a denial of service for services dependent on the interpreter. In more sophisticated attack scenarios involving controlled heap layouts and additional exploitation techniques like information disclosure primitives, this out-of-bounds write could facilitate remote code execution by redirecting control flow to attacker-controlled shellcode or ROP chains constructed from existing library functions within the host process memory space.
Mitigation strategies must focus on rigorous input validation at the point where numeric values are cast into smaller integer types used for array indexing or buffer sizing. Developers should implement explicit checks to ensure that class instance initialization counts do not exceed safe thresholds before proceeding with allocation and population routines. Utilizing static analysis tools capable of detecting integer truncation issues during code review is essential, as is enabling compiler flags such as -ftrapv in GCC/Clang which trigger traps on signed arithmetic overflow, although care must be taken to ensure these do not introduce performance regressions or false positives for unsigned types where wraparound might be intentional. Furthermore, adopting memory-safe languages or employing sanitizers like AddressSanitizer during development and testing phases can help identify such out-of-bounds accesses early in the lifecycle. For end-users, updating to patched versions of Escargot that include fixes for this numeric truncation logic is critical to maintaining system integrity against exploitation attempts targeting JavaScript execution engines. This vulnerability also maps to MITRE ATT&CK techniques related to memory corruption and potential privilege escalation depending on the context in which the engine operates within a larger application architecture.