CVE-2026-54417: Integer Overflow in rxi microtar Causes Denial of Service

Technical summary

CVE-2026-54417 is an integer overflow vulnerability in the mtar_next() function within rxi microtar's src/microtar.c. The function computes the offset to the next tar record using the formula round_up(h.size, 512) + sizeof(mtar_raw_header_t) with 32-bit unsigned integer arithmetic. When h.size is a multiple of 512 and falls within the range 0xFFFFFC01–0xFFFFFE00 (such as 0xFFFFFE00), the addition overflows and wraps to zero. This causes mtar_next() to return the current record's position rather than advance to the next one. Consequently, mtar_find() and any loop iterating through archive entries stall indefinitely on the same record, consuming 100% CPU with no automatic recovery mechanism.

Business impact

Organizations deploying microtar 0.1.0 in archive processing pipelines face availability risk. This includes backup utilities, container image extraction tools, deployment automation, and any microservice that parses untrusted tar archives. An attacker can trigger a denial of service by uploading or serving a malicious tar file, causing the affected process to hang and exhaust CPU resources. This may cascade to service degradation, failed deployments, or denial of legitimate users. The vulnerability requires no authentication or user interaction, making it suitable for remote exploitation.

Affected systems

The vulnerability affects rxi microtar version 0.1.0. Applications and libraries that bundle or depend on this version are in scope. This includes but is not limited to embedded systems, IoT devices, containerized applications, and any software that processes tar archives as part of normal operation. Organizations should audit their dependency trees and build manifests to identify affected components. Versions prior to 0.1.0 or subsequent patches (if released) may not be vulnerable; verify against the vendor advisory or check the latest microtar repository status.

Exploitability

Exploitability is straightforward. The attack requires only crafting a tar archive with specific header sizes and delivering it to an application that uses the vulnerable library. No special privileges, authentication, or user interaction is needed. The attack surface is broad for any networked service that accepts tar files: cloud storage integration endpoints, CI/CD systems, container registries, and backup services. The barrier to weaponization is low; proof-of-concept archive generation is trivial once the integer overflow conditions are understood.

Remediation

Upgrade rxi microtar to a patched version released after this vulnerability's publication. If no patch is available from the upstream project, consider isolating tar processing to a sandboxed subprocess with resource limits (CPU, memory, timeout), or implement input validation to reject tar headers with suspicious size values before parsing. Long-term, replace microtar with a more actively maintained tar library if the rxi project remains unmaintained. Test all patches thoroughly in non-production environments before deployment.

Patch guidance

Consult the rxi microtar project's official repository and release notes for a patched version. Apply the patch to all systems and applications using microtar 0.1.0, including embedded devices, container images, and compiled binaries. Verify the patched version by checking the mtar_next() function logic and running test cases with the malicious tar archive sizes mentioned in the CVE description (e.g., 0xFFFFFE00). Where in-place patching is not feasible (e.g., firmware or read-only deployments), prepare a rollout plan with rollback procedures. Prioritize systems exposed to untrusted tar input.

Detection guidance

Monitor for processes consuming sustained high CPU while performing tar archive operations. Log and alert on unusual mtar_next() call patterns or loops that process the same tar record repeatedly. Implement network-level detection for tar archives with header sizes in the overflow range (0xFFFFFC01–0xFFFFFE00). If possible, add instrumentation to tar processing functions to detect when offset calculations produce zero or wrap values. Capture and retain samples of uploaded or received tar files for forensic analysis if a denial of service event occurs.

Why prioritize this

This vulnerability scores 7.5 CVSS (HIGH) due to remote exploitability, no authentication requirement, and direct availability impact. Although it does not enable code execution or data theft, the guaranteed denial of service and ease of exploitation make it a credible threat to service continuity. Organizations running microtar in production or as a dependency in web services, automation tools, or cloud infrastructure should prioritize patching. The low effort required to craft a malicious tar file elevates practical risk despite the absence of KEV status or known active exploitation.

Risk score, explained

The CVSS 3.1 score of 7.5 reflects: Attack Vector Network (AV:N) — remote delivery via tar file; Attack Complexity Low (AC:L) — no special conditions needed; Privileges Required None (PR:N) — unauthenticated access; User Interaction None (UI:N) — automatic trigger upon archive processing; Scope Unchanged (S:U) — impact confined to affected process; Confidentiality None (C:N); Integrity None (I:N); Availability High (A:H) — uncontrolled CPU consumption and process hang. The score reflects legitimate concern for availability but acknowledges the absence of confidentiality or integrity compromise.

Frequently asked questions