CVE-2026-38753: BusyBox AWK Use-After-Free Vulnerability

CVE-2026-38753 Overview

CVE-2026-38753 is a use-after-free vulnerability [CWE-416] in the awk_sub() function located in editors/awk.c of BusyBox v1.38.0. An attacker can trigger the flaw by supplying a crafted AWK script, causing the process to reference memory after it has been freed. The condition results in a Denial of Service (DoS) against the BusyBox awk applet. BusyBox is widely deployed in embedded Linux systems, IoT devices, and container base images, expanding the potential exposure of vulnerable installations.

Critical Impact
A crafted AWK script processed by a vulnerable BusyBox awk binary can crash the interpreter, disrupting scripts and automation that depend on BusyBox in embedded, container, or minimal Linux environments.

Affected Products

BusyBox v1.38.0 (editors/awk.c, awk_sub() function)
Embedded Linux distributions bundling BusyBox v1.38.0
Container base images using BusyBox v1.38.0 as a userland

Discovery Timeline

2026-07-15 - CVE-2026-38753 published to NVD
2026-07-16 - Last updated in NVD database

Technical Details for CVE-2026-38753

Vulnerability Analysis

The defect resides in awk_sub() inside editors/awk.c, the routine that implements the AWK sub() and gsub() substitution built-ins in BusyBox. During substitution processing, the function operates on memory that has already been released, producing a use-after-free condition. When the freed memory is later dereferenced or written, the process state becomes inconsistent and the awk applet terminates abnormally.

BusyBox is frequently the sole shell and utility provider on constrained systems. A crash in awk interrupts init scripts, network configuration flows, package build pipelines, and orchestration tasks that pipe untrusted input through AWK. The EPSS probability is 0.145%, indicating no observed exploitation activity at time of publication.

Root Cause

The root cause is improper lifetime management of a heap object referenced by awk_sub(). The function retains a pointer to a buffer that is freed during substitution handling, then continues to access that pointer. Specific AWK constructs in the input script drive the code path that reaches the stale reference. Refer to the BusyBox Mailing List Archive for the upstream discussion.

Attack Vector

Exploitation requires the vulnerable BusyBox awk binary to process an attacker-controlled AWK program or an AWK program acting on attacker-controlled input that triggers the substitution path. Delivery vectors include shell scripts on multi-tenant systems, log processing pipelines, CI jobs, and any service that invokes busybox awk on untrusted data. The impact is limited to Denial of Service based on the available advisory data; no code execution has been demonstrated.

No verified proof-of-concept code is published. See the BusyBox Official Website and the upstream mailing list thread for technical follow-up.

Detection Methods for CVE-2026-38753

Indicators of Compromise

Repeated abnormal terminations or segmentation faults from the busybox process when running the awk applet.
Kernel log entries referencing SIGSEGV or SIGABRT for busybox on hosts running v1.38.0.
Failed init or automation scripts that invoke awk on untrusted input, correlated with process crashes.

Detection Strategies

Inventory BusyBox binaries across hosts and container images and flag any instance reporting version 1.38.0.
Monitor for crash signals generated by busybox child processes executing the awk applet.
Inspect CI/CD and log-processing pipelines that feed external data into awk, and alert on unexpected non-zero exit codes.

Monitoring Recommendations

Ingest process termination and core-dump events into a centralized logging or SIEM platform for correlation.
Track BusyBox version metadata in software bill of materials (SBOM) tooling to detect drift onto vulnerable builds.
Add file integrity monitoring on the busybox binary path in embedded and container images to detect unexpected replacements.

How to Mitigate CVE-2026-38753

Immediate Actions Required

Identify all systems, firmware images, and container images shipping BusyBox v1.38.0.
Restrict execution of AWK scripts sourced from untrusted users or external inputs on vulnerable hosts.
Rebuild and redeploy container base images once a fixed BusyBox release is available upstream.

Patch Information

At the time of NVD publication, no fixed BusyBox release is referenced in the advisory. Track the BusyBox Mailing List Archive and the BusyBox Official Website for the patched version, then upgrade all affected systems and images to that release. Rebuild embedded firmware that statically links BusyBox after the fix lands.

Workarounds

Replace the BusyBox awk applet with an alternative AWK implementation such as gawk or mawk on hosts where package size permits.
Sanitize or validate AWK scripts and their inputs before invocation, blocking untrusted sub() and gsub() patterns.
Isolate services that must process untrusted data with awk inside sandboxed containers with restricted resources to contain crash impact.

bash

# Configuration example
# Identify BusyBox version on a host
busybox | head -n 1

# Locate BusyBox binaries across a filesystem
find / -name busybox -type f 2>/dev/null -exec sh -c '"$1" | head -n 1' _ {} \;

# Prefer an alternative AWK implementation when available
command -v gawk >/dev/null && alias awk=gawk