CVE-2026-33645

High

Published: 26 March 2026

Published

26 March 2026

Modified

30 March 2026

KEV Added

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Patch

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

EPSS Score 0.0002 6.3th percentile

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

Summary

CVE-2026-33645 is a high-severity Path Traversal (CWE-22) vulnerability in Shaneisrael Fireshare. Its CVSS base score is 7.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Ingress Tool Transfer (T1105); ranked at the 6.3th 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 Ingress Tool Transfer (T1105) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Requires validation of the checkSum multipart field to sanitize inputs and prevent path traversal during chunked uploads.

SI-2 Flaw Remediation good match

prevent

Mandates timely flaw remediation by upgrading to Fireshare version 1.5.2, which fixes the unsanitized path construction vulnerability.

AC-6 Least Privilege partial match

prevent

Enforces least privilege on the Fireshare process to limit writable paths and reduce the impact of arbitrary file writes.

MITRE ATT&CK Enterprise TechniquesAI

T1105 Ingress Tool Transfer Command And Control

Adversaries may transfer tools or other files from an external system into a compromised environment.

attack.mitre.org →

T1565.001 Stored Data Manipulation Impact

Adversaries may insert, delete, or manipulate data at rest in order to influence external outcomes or hide activity, thus threatening the integrity of the data.

attack.mitre.org →

Why these techniques?

Path traversal in chunked upload enables direct arbitrary file write to writable paths, facilitating tool/payload ingress (T1105) and stored data manipulation such as config overwrites (T1565.001).

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

NVD Description

Fireshare facilitates self-hosted media and link sharing. In version 1.5.1, an authenticated path traversal vulnerability in Fireshare’s chunked upload endpoint allows an attacker to write arbitrary files outside the intended upload directory. The `checkSum` multipart field is used directly in…

filesystem path construction without sanitization or containment checks. This enables unauthorized file writes to attacker-chosen paths writable by the Fireshare process (e.g., container `/tmp`), violating integrity and potentially enabling follow-on attacks depending on deployment. Version 1.5.2 fixes the issue.

Deeper analysisAI

CVE-2026-33645 is an authenticated path traversal vulnerability (CWE-22, CWE-73) affecting Fireshare version 1.5.1, a self-hosted media and link sharing application. The issue resides in the chunked upload endpoint, where the `checkSum` multipart field is used directly in filesystem path construction without sanitization or containment checks. This allows attackers to write arbitrary files outside the intended upload directory to paths writable by the Fireshare process, such as `/tmp` in containerized deployments. The vulnerability has a CVSS v3.1 base score of 7.1 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L), indicating high integrity impact with low availability impact and no confidentiality impact.

An authenticated attacker with low privileges can exploit this vulnerability over the network with low complexity and no user interaction required. By manipulating the `checkSum` field during a chunked upload, they can direct file writes to arbitrary locations accessible to the process, violating filesystem integrity and potentially enabling follow-on attacks based on the deployment environment, such as overwriting configuration files or staging payloads in shared directories.

GitHub security advisories (GHSA-7q8r-vpq3-89m7) and the release notes for Fireshare version 1.5.2 confirm that the issue is fixed in the updated version, recommending an immediate upgrade to mitigate the vulnerability.