CVE-2026-47307: Samsung Walrus DoS Vulnerability

CVE-2026-47307 Overview

CVE-2026-47307 is a NULL pointer dereference vulnerability [CWE-476] in Samsung Open Source Walrus, a WebAssembly runtime. An attacker can trigger a denial of service by supplying a crafted WebAssembly module containing deeply nested instructions. The flaw affects Walrus at commit f339b8ee4ea701772e8ae640b3d1b12ac02b1ae9. Exploitation requires local access and user interaction to load the malicious module. Successful exploitation crashes the Walrus runtime process, disrupting any application that depends on it.

Critical Impact

A crafted WebAssembly module causes the Walrus runtime to dereference a NULL pointer, terminating the process and producing a high-impact availability loss on the affected host.

Affected Products

• Samsung Open Source Walrus at commit f339b8ee4ea701772e8ae640b3d1b12ac02b1ae9
• Applications embedding the vulnerable Walrus WebAssembly runtime
• Downstream builds that have not merged the upstream fix

Discovery Timeline

• 2026-05-19 - CVE-2026-47307 published to NVD
• 2026-05-19 - Last updated in NVD database

Technical Details for CVE-2026-47307

Vulnerability Analysis

Walrus is a WebAssembly runtime maintained by Samsung Open Source. The vulnerability sits in the module parsing and validation path that processes WebAssembly instruction sequences. When a module contains instructions nested beyond the depth the runtime anticipates, an internal pointer used during parsing is left unset. The runtime later dereferences this NULL pointer, causing an immediate process crash.

The issue is a classic NULL pointer dereference [CWE-476] rather than a memory corruption primitive. Confidentiality and integrity are not affected. The impact is limited to availability, but availability loss is total for the runtime process.

The attacker delivers the trigger through a crafted .wasm module. Exploitation requires a local user to load or execute the malicious module within Walrus, which aligns with the local attack vector and required user interaction.

Root Cause

The runtime does not enforce a safe upper bound on instruction nesting depth during module decoding. When recursion or stack-based traversal exceeds expected limits, an internal data structure pointer remains uninitialized. Subsequent code paths assume the pointer is valid and dereference it without a NULL check. The upstream fix is tracked in the Samsung Walrus pull request 409.

Attack Vector

An attacker crafts a WebAssembly module with deeply nested control-flow instructions such as block, loop, or if constructs. The victim loads the module into an application that embeds Walrus. During parsing or validation, the runtime hits the unguarded code path and crashes. No privileges are required, but user interaction is needed to load the module. See the upstream pull request for the corrected validation logic.

Detection Methods for CVE-2026-47307

Indicators of Compromise

• Unexpected termination of processes embedding the Walrus runtime shortly after loading a .wasm file
• Crash dumps showing a NULL pointer dereference within Walrus module parsing or validation functions
• WebAssembly modules from untrusted sources containing abnormally deep nesting of block, loop, or if instructions

Detection Strategies

• Inspect inbound WebAssembly modules with a parser that reports maximum nesting depth and flag modules exceeding reasonable thresholds
• Monitor application logs for repeated Walrus runtime crashes correlated with module loads
• Hash and inventory .wasm artifacts deployed in production to detect unexpected or unsigned modules

Monitoring Recommendations

• Enable operating system crash reporting for any process embedding Walrus and forward reports to a central log store
• Alert on segmentation faults or SIGSEGV signals raised by Walrus-linked binaries
• Track the build hash of Walrus in software inventory to confirm the patched commit is deployed

How to Mitigate CVE-2026-47307

Immediate Actions Required

• Update Walrus to a build that includes the fix merged through Samsung Walrus pull request 409
• Restrict loading of WebAssembly modules to trusted, signed sources only
• Audit applications embedding Walrus and identify those running the vulnerable commit f339b8ee4ea701772e8ae640b3d1b12ac02b1ae9

Patch Information

The maintainers addressed the issue in the upstream repository. Rebuild Walrus from a revision that includes the merged fix referenced in the GitHub pull request, then redeploy any application that statically or dynamically links the runtime.

Workarounds

• Validate WebAssembly modules before execution and reject modules with instruction nesting depth beyond an enforced limit
• Run Walrus-embedding applications under process supervisors that isolate crashes from other workloads
• Disable WebAssembly module loading in untrusted contexts until the patched build is deployed

# Configuration example: rebuild Walrus from a patched revision
git clone https://github.com/Samsung/walrus.git
cd walrus
git fetch origin pull/409/head:fix-null-deref
git checkout fix-null-deref
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build