CVE-2026-39973

High

Published: 21 April 2026

Published

21 April 2026

Modified

23 April 2026

KEV Added

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Patch

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CVSS Score 7.1 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

EPSS Score 0.0001 1.6th percentile

Risk Priority 14 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-39973 is a high-severity Path Traversal (CWE-22) vulnerability in Apktool Apktool. Its CVSS base score is 7.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Malicious File (T1204.002); ranked at the 1.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Malicious File (T1204.002) and 2 other techniques. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Timely flaw remediation through patching Apktool to version 3.0.2 directly eliminates the path traversal vulnerability by restoring path sanitization.

SI-10 Information Input Validation good match

prevent

Requires validation of untrusted inputs from APK resources.arsc string pools to block ../ traversal sequences before filesystem writes.

SI-7 Software, Firmware, and Information Integrity partial match

detect

Performs software integrity checks and monitors for unauthorized file modifications resulting from path traversal exploitation during decoding.

MITRE ATT&CK Enterprise TechniquesAI

T1204.002 Malicious File Execution

An adversary may rely upon a user opening a malicious file in order to gain execution.

attack.mitre.org →

T1547.001 Registry Run Keys / Startup Folder Persistence

Adversaries may achieve persistence by adding a program to a startup folder or referencing it with a Registry run key.

attack.mitre.org →

T1546.004 Unix Shell Configuration Modification Privilege Escalation

Adversaries may establish persistence through executing malicious commands triggered by a user’s shell.

attack.mitre.org →

Why these techniques?

Path traversal in APK decoding enables arbitrary file writes from a malicious APK (facilitating T1204.002 Malicious File when victim runs apktool d), which directly supports persistence via writes to Windows startup folders (T1547.001) or Unix shell configs like .bashrc (T1546.004).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v18.1

NVD Description

Apktool is a tool for reverse engineering Android APK files. In versions 3.0.0 and 3.0.1, a path traversal vulnerability in `brut/androlib/res/decoder/ResFileDecoder.java` allows a maliciously crafted APK to write arbitrary files to the filesystem during standard decoding (`apktool d`). This is…

a security regression introduced in commit e10a045 (PR #4041, December 12, 2025), which removed the `BrutIO.sanitizePath()` call that previously prevented path traversal in resource file output paths. An attacker can embed `../` sequences in the `resources.arsc` Type String Pool to escape the output directory and write files to arbitrary locations, including `~/.ssh/config`, `~/.bashrc`, or Windows Startup folders, escalating to RCE. The fix in version 3.0.2 re-introduces `BrutIO.sanitizePath()` in `ResFileDecoder.java` before file write operations.

Deeper analysisAI

CVE-2026-39973 is a path traversal vulnerability (CWE-22) affecting Apktool versions 3.0.0 and 3.0.1, a tool used for reverse engineering Android APK files. The issue resides in the `brut/androlib/res/decoder/ResFileDecoder.java` component and enables a maliciously crafted APK to write arbitrary files to the filesystem during standard decoding operations with the `apktool d` command. This flaw represents a security regression introduced by commit e10a045 (PR #4041, dated December 12, 2025), which removed the `BrutIO.sanitizePath()` call previously used to prevent path traversal in resource file output paths. The vulnerability has a CVSS v3.1 base score of 7.1 (AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N).

An attacker can exploit this vulnerability locally by providing a victim with a specially crafted APK containing `../` sequences embedded in the `resources.arsc` Type String Pool. If the victim, such as a security researcher or reverse engineer, runs `apktool d` on the malicious APK, it escapes the intended output directory and writes files to arbitrary locations on the filesystem. Potential targets include sensitive paths like `~/.ssh/config`, `~/.bashrc` on Unix-like systems, or Windows Startup folders, potentially leading to remote code execution (RCE) through privilege escalation or persistent access.

Mitigation is available via upgrade to Apktool version 3.0.2, which re-introduces the `BrutIO.sanitizePath()` function in `ResFileDecoder.java` prior to file write operations. Official advisories and resources, including the GitHub security advisory (GHSA-m8mh-x359-vm8m), release notes for v3.0.2, the original pull request #4041, and the regressing commit e10a045, detail the issue and fix for practitioners to review and apply.