CVE-2026-4424

What it actually does

The vulnerability is a heap out-of-bounds read in libarchive's RAR decompression logic. When processing a specially crafted RAR archive, improper validation of the LZSS sliding-window size after switching between compression methods can cause libarchive to read memory outside the intended heap buffer. The primary impact is confidentiality loss: data present in adjacent heap memory may be exposed to the attacker through the archive-processing workflow. The flaw does not directly provide code execution, privilege escalation, or data modification based on the available description, but it can leak sensitive process memory such as file fragments, metadata, tokens, service data, or other in-process secrets depending on what application embeds libarchive and how archive parsing results are returned or observable.

Why it matters to the business

Organizations using libarchive directly or through platforms such as Red Hat Enterprise Linux, Red Hat OpenShift Container Platform, Red Hat hardened images, or applications that automatically inspect or extract archives may face unauthorized disclosure of sensitive information. The practical business risk is highest where untrusted RAR files are accepted from external users, email attachments, web uploads, CI/CD artifacts, container images, package repositories, malware sandboxes, or document-processing pipelines. Although this vulnerability is not currently listed in CISA KEV, is not known to be used in ransomware campaigns, and has a low reported EPSS score, the attack requires no authentication and no user interaction when exposed archive-processing services automatically parse attacker-supplied files, making remediation important for internet-facing or high-volume file-processing systems.

How an attack unfolds

An attacker creates a malformed RAR archive designed to trigger an invalid LZSS sliding-window state during transitions between RAR compression methods. The attacker then delivers the archive to a system or service that uses libarchive to inspect, validate, index, unpack, scan, or otherwise process RAR files. If the vulnerable code path is reached, libarchive reads beyond the intended heap buffer. Depending on the calling application, the out-of-bounds bytes may be returned in extracted output, error handling, logs, previews, scanning results, or another observable response. The attacker collects that leaked data and analyzes it for sensitive memory contents. Exploitation is most plausible against automated archive-processing services because the flaw does not require a local account or an interactive victim when the service processes attacker-controlled archives automatically.

How to fix it

Upgrade libarchive and any vendor packages that embed or statically link libarchive to versions containing the vendor fix when available. Because no fixed versions were provided in the input, follow the relevant vendor advisories for Red Hat Enterprise Linux, Red Hat Enterprise Linux Server AUS, Red Hat OpenShift Container Platform, OpenShift variants for ARM64 and Power, and Red Hat hardened images. Rebuild and redeploy containers, appliances, and applications that include vulnerable libarchive libraries, including statically linked binaries. If immediate patching is not possible, reduce exposure by disabling RAR extraction or inspection where not business-critical, blocking RAR uploads from untrusted users, routing archive handling through isolated sandboxes with no sensitive in-memory context, enforcing strict file type allowlists, limiting returned parser output, and ensuring archive-processing services run with least privilege and memory-safe isolation boundaries.

How to confirm the fix worked

Confirm remediation by inventorying libarchive versions across operating systems, containers, application images, and statically bundled dependencies, then comparing them with the fixed versions published by the applicable vendors. On Linux systems, use package-manager queries and image scans to identify installed libarchive packages, and use software composition analysis for applications that vendor or statically link libarchive. Validate that patched container base images have been rebuilt and redeployed rather than only updated in source repositories. Where safe and authorized, run a controlled regression test using a benign proof-of-concept or vendor-provided test case to confirm the RAR parser no longer performs the invalid read. Also verify compensating controls by attempting to upload or process RAR files through exposed workflows and confirming they are rejected, quarantined, or handled only in an isolated environment.

Typical attack path

1. Identify an application, appliance, container platform component, scanning service, upload portal, CI/CD workflow, or backend job that processes RAR archives using libarchive.
2. Craft or obtain a malformed RAR file that manipulates compression-method transitions and LZSS sliding-window state to trigger the heap out-of-bounds read.
3. Submit the archive through an exposed upload, API, email-processing path, artifact repository, container/image scanning workflow, or other automated file-processing channel.
4. Cause the vulnerable libarchive RAR parser to process the malicious archive.
5. Observe responses, generated files, extraction output, scanner output, logs, or side-channel artifacts that may contain leaked heap memory.
6. Repeat with adjusted archive structure if necessary to improve reliability or target useful memory disclosure.

How to detect it

To assess whether exploitation already occurred, review telemetry from systems and applications that process RAR archives using libarchive. Focus on web upload logs, API gateway logs, WAF events, email gateway logs, object-storage access logs, artifact repository logs, CI/CD job logs, antivirus or malware-scanning logs, container/image scanning logs, application extraction logs, and system crash or sanitizer logs. Look for RAR files submitted by untrusted sources shortly before abnormal parser behavior, repeated failed extraction attempts, malformed archive errors, unexpected binary data in extraction output, unusually large or corrupted extraction results, and responses that may have exposed memory-like content. Correlate suspicious archive submissions with process crashes, core dumps, heap-checker findings, segmentation faults, or service restarts involving archive-handling processes. If possible, preserve submitted RAR samples, request/response bodies, generated extraction output, worker logs, and memory dumps for forensic analysis. There are no public actor-specific or campaign-specific indicators provided for this vulnerability, so detection should be behavior-based rather than relying on known malicious hashes or infrastructure.

What your security team should do

• Prioritize patching internet-facing, externally fed, or automated file-processing services that accept RAR archives or inspect arbitrary uploaded files.
• Inventory libarchive usage across servers, container images, CI/CD tooling, artifact scanners, email gateways, malware sandboxes, document-processing services, and application dependencies.
• Track Red Hat and upstream libarchive advisories for exact fixed package versions and apply updates as soon as they are available for affected platforms.
• Rebuild and redeploy all affected container images and application packages after updating base images or linked libraries.
• Temporarily disable or block RAR processing from untrusted sources where business processes allow.
• Run archive parsing in sandboxed, low-privilege workers with minimal access to secrets and sensitive in-memory data.
• Limit verbose extraction errors, parser output, and diagnostic logs that could expose leaked memory contents to external users.
• Add monitoring for unusual RAR upload or processing activity, especially malformed archives, repeated parser failures, and probing of upload endpoints.
• Use SCA and container scanning to detect bundled or statically linked libarchive copies that package managers may not report.
• Because this issue is not currently KEV-listed and has low EPSS, balance urgency against exposure: prioritize externally reachable archive-processing paths first, then internal and low-risk systems.