CVE-2026-86315 Overview
CVE-2026-86315 is an out-of-bounds write vulnerability in Samsung's Open Source Escargot JavaScript engine on Linux x86-64. The flaw stems from numeric truncation [CWE-197] when the engine processes a crafted class definition whose instance initialization entry count exceeds UINT16_MAX. An attacker who can supply JavaScript for execution can corrupt native memory and crash the host process. The issue affects Escargot commit 5dc93606abd42b859045add05d704a038e197359.
Critical Impact
Attackers with the ability to execute JavaScript in an Escargot-embedded application can trigger native memory corruption and terminate the host process, resulting in a local denial-of-service condition.
Affected Products
- Samsung Open Source Escargot JavaScript engine
- Commit 5dc93606abd42b859045add05d704a038e197359
- Linux x86-64 builds of Escargot
Discovery Timeline
- 2026-09-07 - CVE-2026-86315 published to NVD
- 2026-09-08 - Last updated in NVD database
Technical Details for CVE-2026-86315
Vulnerability Analysis
Escargot is Samsung's lightweight JavaScript engine designed for embedded and IoT environments. The vulnerability arises during class definition parsing, specifically in the handling of instance initialization entries. The engine stores the entry count in a 16-bit unsigned integer. When a class definition contains more entries than UINT16_MAX (65,535), the value is truncated during assignment.
The truncated count is later used to allocate and index a native buffer. Because the allocation reflects the truncated value while subsequent write operations use the untruncated intent, the engine writes past the end of the allocated region. This corrupts adjacent heap memory and crashes the host process on Linux x86-64.
Root Cause
The root cause is a numeric truncation error [CWE-197] where a larger integer type is narrowed to a 16-bit unsigned integer without validating the source value. The class definition path does not enforce an upper bound on instance initialization entries before performing the narrowing conversion, breaking the invariant between the stored count and the actual number of entries processed.
Attack Vector
Exploitation requires the attacker to supply JavaScript to an application that embeds Escargot. The attack vector is local and requires no privileges or user interaction, but the impact is limited to availability. The attacker crafts a class definition containing more than 65,535 instance initialization entries, triggering the truncation and the resulting out-of-bounds write during class instantiation.
Refer to the GitHub Pull Request for Escargot for the technical fix and additional context on the vulnerable code path.
Detection Methods for CVE-2026-86315
Indicators of Compromise
- Unexpected crashes or SIGSEGV termination in processes embedding Escargot after executing untrusted JavaScript.
- Core dumps referencing class definition parsing or instance initialization logic within Escargot.
- JavaScript payloads containing class definitions with abnormally large numbers of field initializers or class members.
Detection Strategies
- Inspect JavaScript inputs delivered to Escargot-embedded services for class definitions containing more than 65,535 instance initialization entries.
- Monitor host telemetry for abnormal termination of processes that embed Escargot, correlating crash times with recent script execution.
- Enable ASan or similar memory sanitizers in development and test builds of Escargot to surface out-of-bounds writes triggered by fuzzed inputs.
Monitoring Recommendations
- Forward process-crash events and core dump metadata from Linux hosts running Escargot workloads to a centralized logging or SIEM platform.
- Track the size and structure of JavaScript payloads accepted by applications embedding Escargot, alerting on outliers.
- Review commit hashes of deployed Escargot builds against the vulnerable revision 5dc93606abd42b859045add05d704a038e197359.
How to Mitigate CVE-2026-86315
Immediate Actions Required
- Identify all applications and devices that embed Escargot and enumerate their commit or version.
- Restrict execution of untrusted JavaScript in Escargot-embedded services until a fixed build is deployed.
- Rebuild affected components after pulling the upstream fix referenced in the Escargot repository.
Patch Information
The fix is tracked in the GitHub Pull Request for Escargot. Rebuild Escargot from a commit that includes this change and redistribute the updated binaries to affected embedded and Linux x86-64 deployments.
Workarounds
- Validate and reject class definitions whose instance initialization entry counts approach or exceed UINT16_MAX before passing scripts to the engine.
- Sandbox Escargot host processes so that a crash does not affect adjacent services on the same host.
- Constrain JavaScript input sources to trusted origins where feasible until the patched build is in place.
# Verify the Escargot commit in a build tree
cd /path/to/escargot
git log -1 --format=%H
# If output matches 5dc93606abd42b859045add05d704a038e197359, update:
git fetch origin
git checkout main
git pull --ff-only
# Rebuild per project instructions
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.