CVE-2021-38297: Golang Go Buffer Overflow Vulnerability

CVE-2021-38297 Overview

CVE-2021-38297 is a critical buffer overflow vulnerability affecting Go programming language versions before 1.16.9 and 1.17.x before 1.17.2. The vulnerability occurs when large arguments are passed in a function invocation from a WebAssembly (WASM) module when compiled with GOARCH=wasm and GOOS=js settings.

This buffer overflow condition allows attackers to potentially execute arbitrary code or cause denial of service conditions by exploiting the improper handling of oversized arguments during WASM function calls.

Critical Impact

This vulnerability enables remote attackers to trigger a buffer overflow through maliciously crafted WASM module function calls, potentially leading to arbitrary code execution, memory corruption, or complete system compromise in affected Go applications.

Affected Products

• Golang Go versions prior to 1.16.9
• Golang Go versions 1.17.x prior to 1.17.2
• Fedora Project Fedora 34 and 35 (via bundled Go packages)

Discovery Timeline

• 2021-10-18 - CVE-2021-38297 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-38297

Vulnerability Analysis

The vulnerability resides in Go's WebAssembly runtime implementation. When Go code is compiled to WebAssembly using the GOARCH=wasm and GOOS=js environment variables, the resulting WASM module contains a runtime that handles function invocations between JavaScript and Go code.

The flaw occurs during the processing of function arguments passed from the WASM module. When exceptionally large arguments are provided during a function invocation, the Go runtime fails to properly validate the argument size before copying data into a fixed-size buffer. This lack of bounds checking leads to a classic buffer overflow condition (CWE-120).

The network-based attack vector makes this particularly dangerous for web applications and services that execute Go-compiled WASM modules in browser or server-side JavaScript environments. An attacker can craft malicious inputs that trigger the overflow remotely without requiring authentication or user interaction.

Root Cause

The root cause is improper input validation in the Go WASM runtime's argument handling code. When processing function invocation arguments from the WASM module, the runtime does not adequately verify that the argument size fits within allocated buffer boundaries. This allows an attacker to supply arguments that exceed the expected maximum size, causing memory to be written beyond the intended buffer limits.

The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), which describes scenarios where data is copied to a buffer without first checking that the data will fit within the buffer's capacity.

Attack Vector

The attack vector for CVE-2021-38297 is network-based and requires no privileges or user interaction. An attacker can exploit this vulnerability by:

1. Targeting a web application or service that uses Go code compiled to WebAssembly
2. Crafting a malicious WASM function call with oversized arguments
3. Triggering the buffer overflow when the Go runtime processes the arguments
4. Potentially achieving arbitrary code execution or causing a denial of service

The exploitation mechanism involves passing excessively large arguments through the WASM module's function invocation interface. When these arguments are processed by the vulnerable Go runtime, the buffer overflow occurs, potentially overwriting adjacent memory regions including return addresses or other critical data structures.

For technical details on the vulnerability mechanism, see the Golang Announce Message.

Detection Methods for CVE-2021-38297

Indicators of Compromise

• Unexpected crashes or segmentation faults in Go applications compiled to WASM
• Memory corruption errors in browser JavaScript consoles when running Go WASM modules
• Abnormal memory usage patterns in applications utilizing Go WASM modules
• Application logs showing unusual function call patterns with large argument sizes

Detection Strategies

• Implement version checking for Go runtime in deployed WASM modules to identify vulnerable versions (< 1.16.9 or 1.17.x < 1.17.2)
• Deploy web application firewalls (WAF) to monitor for abnormally large payloads targeting WASM endpoints
• Use application security monitoring to detect memory corruption attempts or unusual crash patterns
• Integrate static analysis tools to identify Go applications compiled with vulnerable versions

Monitoring Recommendations

• Monitor application logs for crashes related to WASM function invocations
• Set up alerts for memory consumption anomalies in services running Go WASM modules
• Implement runtime application self-protection (RASP) to detect buffer overflow attempts
• Enable browser console logging and monitoring for client-side Go WASM applications

How to Mitigate CVE-2021-38297

Immediate Actions Required

• Upgrade Go to version 1.16.9 or 1.17.2 or later immediately
• Recompile all WASM modules using the patched Go version
• Audit deployed applications to identify those using Go WASM compilation
• Consider temporarily disabling affected WASM modules until patches can be applied

Patch Information

The Go team has released patched versions to address this vulnerability. Users should upgrade to Go 1.16.9 or 1.17.2 (or later versions) to remediate this issue. After upgrading, all WASM modules must be recompiled using the patched Go toolchain.

For additional information, refer to the following security advisories:

• Golang Announce Message
• Gentoo GLSA Advisory
• NetApp Security Advisory
• Debian LTS Announcement

Workarounds

• Avoid using GOARCH=wasm and GOOS=js compilation targets until patching is complete
• Implement input validation at the JavaScript layer before invoking WASM functions
• Deploy network-level controls to limit payload sizes to WASM endpoints
• Consider sandboxing WASM execution environments to limit potential impact

# Upgrade Go to patched version
go version  # Check current version
# Download and install Go 1.16.9+ or 1.17.2+
# Recompile WASM modules
GOARCH=wasm GOOS=js go build -o app.wasm ./main.go