CVE-2026-58303: Escargot Buffer Overflow Vulnerability

CVE-2026-58303 Overview

CVE-2026-58303 is a stack-based buffer overflow [CWE-121] in Samsung Open Source Escargot, a lightweight JavaScript engine used in memory-constrained environments and embedded systems. The flaw affects all Escargot builds prior to commit b30b63fc63b403907d8137da1c65aaa4521fe74e. An attacker who convinces a user to execute a crafted JavaScript payload can corrupt stack memory, causing process termination and potential integrity impact within the interpreter context.

Critical Impact
Local attackers can trigger a stack overflow in the Escargot JavaScript engine by supplying malicious script input, resulting in high availability impact and limited integrity impact on the affected process.

Affected Products

Samsung Open Source Escargot JavaScript engine
Escargot versions before commit b30b63fc63b403907d8137da1c65aaa4521fe74e
Downstream applications and embedded devices bundling vulnerable Escargot builds

Discovery Timeline

2026-07-09 - CVE-2026-58303 published to the National Vulnerability Database (NVD)
2026-07-09 - Last updated in NVD database

Technical Details for CVE-2026-58303

Vulnerability Analysis

Escargot is Samsung's ECMAScript engine designed for constrained targets such as IoT devices. The engine parses and executes JavaScript through a set of internal routines that manage evaluation stacks and call frames. A stack-based buffer overflow condition exists in these routines when handling specifically crafted input, allowing writes beyond the allocated stack buffer boundary.

Exploitation requires local access and user interaction, typically in the form of loading or executing a malicious JavaScript file within an application embedding Escargot. Successful exploitation reliably crashes the host process, and depending on stack layout and compiler mitigations, may permit limited manipulation of adjacent stack data.

The issue is tracked upstream in the GitHub Issue Report and resolved through the GitHub Pull Request.

Root Cause

The root cause is missing or insufficient bounds checking on a stack-allocated buffer during JavaScript processing. Input-derived size or index values are used without validation against the buffer's fixed capacity, allowing sequential writes to exceed the buffer and corrupt the return address, saved registers, or adjacent locals on the call stack [CWE-121].

Attack Vector

The attack vector is local and requires user interaction. An attacker crafts a malicious JavaScript file and delivers it to a user or application that loads scripts through Escargot. When the engine parses or evaluates the payload, the overflow occurs. There is no network-based path, and no elevated privileges are required to trigger the condition.

No verified proof-of-concept code has been published. Refer to the upstream issue and patch for technical details on the vulnerable code path.

Detection Methods for CVE-2026-58303

Indicators of Compromise

Unexpected crashes or segmentation faults in processes linking against libescargot or embedding the Escargot interpreter
Core dumps showing stack corruption originating in Escargot parser or evaluator frames
Delivery of unsolicited or obfuscated .js files to systems running Escargot-based applications

Detection Strategies

Inventory all applications, firmware images, and containers that ship Escargot and identify builds predating commit b30b63fc63b403907d8137da1c65aaa4521fe74e
Enable stack canary and AddressSanitizer builds in development and QA to surface overflow behavior during script fuzzing
Correlate process crash telemetry with recent JavaScript file access or IPC events involving the Escargot runtime

Monitoring Recommendations

Collect and centralize crash reports from endpoints and embedded devices running Escargot for review against this CVE
Monitor filesystem and application logs for the introduction of new or modified JavaScript files consumed by Escargot-based processes
Track upstream Samsung Escargot commits and releases to identify regressions or related parser issues

How to Mitigate CVE-2026-58303

Immediate Actions Required

Update Escargot to a build that includes commit b30b63fc63b403907d8137da1c65aaa4521fe74e or later
Rebuild and redistribute any downstream products, firmware, or containers that statically link the vulnerable Escargot version
Restrict which users and processes can supply JavaScript input to Escargot-based applications until patching is complete

Patch Information

The fix is available upstream in the Samsung Escargot repository. Consumers should pull sources at or after commit b30b63fc63b403907d8137da1c65aaa4521fe74e and rebuild. Review the GitHub Pull Request for the exact code changes and validation logic added around the affected buffer.

Workarounds

Disable or gate execution of untrusted JavaScript in applications embedding Escargot until the patched version is deployed
Sandbox Escargot-hosting processes with reduced privileges and strict filesystem access to limit blast radius on crash
Enforce compiler hardening flags such as stack protectors and non-executable stack in downstream builds of Escargot

bash

# Rebuild Escargot from a patched revision
git clone https://github.com/Samsung/escargot.git
cd escargot
git checkout b30b63fc63b403907d8137da1c65aaa4521fe74e
cmake -H. -Bout/release -DESCARGOT_HOST=linux -DESCARGOT_ARCH=x64 -DESCARGOT_MODE=release
cmake --build out/release