CVE-2026-86314: Samsung Walrus WebAssembly DOS Vulnerability

CVE-2026-86314 is a denial of service flaw in Samsung Walrus WebAssembly runtime caused by integer overflow in memory bounds checking. Attackers can exploit this to trigger out-of-bounds heap reads. This article covers technical details, affected versions, impact assessment, and mitigation strategies.

CVE-2026-86314 Overview

CVE-2026-86314 is an integer overflow vulnerability in Samsung Walrus, a WebAssembly runtime. The flaw resides in the source-bounds check inside Memory::init() located at src/runtime/Memory.cpp. A 32-bit unsigned addition wraps around and bypasses the bounds check, allowing a crafted WebAssembly module to trigger an out-of-bounds heap read. The condition leads to denial of service and potential exposure of adjacent heap memory. The issue affects Walrus at commit ff3bf5ff5c4878f8e5572c9593d303f6bc997443 and is tracked under CWE-190.

Critical Impact
A remote attacker delivering a crafted WebAssembly module can cause an out-of-bounds heap read and crash the Walrus runtime, disrupting any host application embedding it.

Affected Products

Samsung Walrus WebAssembly runtime
Walrus commit ff3bf5ff5c4878f8e5572c9593d303f6bc997443
All platforms where Walrus is embedded

Discovery Timeline

2026-09-07 - CVE-2026-86314 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-86314

Vulnerability Analysis

Samsung Walrus is a lightweight WebAssembly (Wasm) virtual machine. The Memory::init() function implements the Wasm memory.init instruction, which copies bytes from a passive data segment into linear memory. Before performing the copy, the function validates that the source offset plus the requested length remain within the data segment size.

The check uses 32-bit unsigned arithmetic. When an attacker supplies a large source offset and length whose sum exceeds UINT32_MAX, the addition wraps to a small value that passes the comparison. The runtime then dereferences memory beyond the data segment boundary, reading adjacent heap contents into linear memory or crashing the process. The vulnerability is limited to availability impact and requires a local attack vector, since the malicious module must be loaded by the host embedding Walrus.

Root Cause

The root cause is unchecked 32-bit unsigned addition in the source-bounds validation logic inside src/runtime/Memory.cpp. The developer compared source_offset + length against the segment size without first checking for arithmetic overflow. The correct pattern promotes operands to 64-bit or validates that length <= segment_size - source_offset before the addition.

Attack Vector

Exploitation requires the victim to load an attacker-controlled WebAssembly module into a host application built on Walrus. The module declares a passive data segment and issues a memory.init instruction with crafted offset and length immediates whose sum overflows a 32-bit unsigned integer. Walrus accepts the operands as valid, then performs an out-of-bounds heap read while copying into linear memory. The result is either a runtime crash or leakage of adjacent heap bytes into the guest's linear memory. See the GitHub Pull Request #482 for the corrected bounds-check logic.

Detection Methods for CVE-2026-86314

Indicators of Compromise

Unexpected termination or segmentation faults in processes embedding the Walrus runtime
Crash reports referencing Memory::init or src/runtime/Memory.cpp stack frames
Loading of untrusted WebAssembly modules containing passive data segments with unusually large memory.init offset or length immediates

Detection Strategies

Enable AddressSanitizer or heap-guard instrumentation in Walrus test builds to surface out-of-bounds reads during module validation
Statically scan Wasm modules for memory.init instructions whose operands approach UINT32_MAX before loading them into production
Monitor host applications for repeated crashes correlated with Wasm module ingestion events

Monitoring Recommendations

Aggregate process crash telemetry from hosts running Walrus-based workloads and alert on repeated faults in the runtime
Log every WebAssembly module load with source identity, size, and hash to support post-incident triage
Track outbound execution of Wasm modules originating from untrusted sources or user-supplied content

How to Mitigate CVE-2026-86314

Immediate Actions Required

Update Walrus to a revision that includes the fix merged in GitHub Pull Request #482
Rebuild and redeploy every host application that statically links or embeds the vulnerable Walrus commit
Restrict Wasm module ingestion to trusted sources until patched binaries are in place

Patch Information

The fix is available in Samsung Walrus Pull Request #482, which corrects the source-bounds validation in Memory::init() to prevent 32-bit unsigned overflow. Downstream projects embedding Walrus should pin to a commit that contains the merged patch and rebuild affected binaries.

Workarounds

Reject or sandbox WebAssembly modules from untrusted origins until Walrus is patched
Run Walrus-embedded processes under strict resource and privilege isolation so a crash does not affect other services
Apply pre-load static analysis that rejects modules containing memory.init operands whose sum would overflow UINT32_MAX

bash

# Update Walrus to a patched revision and rebuild
cd walrus
git fetch origin
git checkout main
git pull origin main
# Confirm PR #482 is present in history
git log --oneline | grep -i "Memory::init"
cmake -B build -S . && cmake --build build