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Strapi Upload Plugin MIME Validation Bypass via Content API

Moderate severity GitHub Reviewed Published May 13, 2026 in strapi/strapi • Updated May 15, 2026

Package

npm @strapi/upload (npm)

Affected versions

<= 5.33.2

Patched versions

5.33.3

Description

Summary of CVE-2026-22707 Vulnerability Details

  • CVE: CVE-2026-22707
  • CVSS v3.1 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N (5.3 — Medium)
  • Affected Versions: @strapi/upload <=5.33.2
  • How to Patch: Immediately update your Strapi to >=5.33.3

Description of CVE-2026-22707

In Strapi versions prior to 5.33.3, the Upload plugin's Content API endpoints did not enforce the administrator-configured MIME type restrictions (plugin.upload.security.allowedTypes and deniedTypes). The same restrictions were correctly enforced on the Admin Panel upload path.

The upload plugin's enforceUploadSecurity security check was invoked in the admin upload controller but was missing from the Content API controller. The Content API handlers uploadFiles and replaceFile (and the upload wrapper that dispatches to them) called the underlying upload service directly, bypassing both the magic-byte MIME detection and the configured allow/deny lists.

An authenticated user with the Content API upload permission could therefore upload file types the administrator had explicitly disallowed, including HTML and SVG content. In deployments serving uploaded files from the same origin as the admin panel (default), an attacker could upload an HTML or SVG file that, when opened directly by an admin, executed JavaScript in the admin origin, enabling admin-session hijack and authenticated administrative actions against the admin API.

The patch introduces a shared prepareUploadRequest helper that wraps enforceUploadSecurity and is called from both the Content API and admin upload controllers, ensuring identical security policy enforcement on every upload entry point.

IoC's for CVE-2026-22707

Indicators that an instance running an unpatched version may have been exploited:

  • Files in /uploads/ with extensions outside the configured allow-list, particularly .html, .htm, .svg, .js, .mjs, .xml, or .xhtml. Filesystem regex: \.(html?|svg|m?js|x?html|xml)$
  • Successful 201 responses from POST /api/upload where the uploaded file's MIME or extension is outside the configured allowedTypes
  • Server access logs showing non-administrator users uploading files with executable web content types. Content-Type regex: text/html|application/javascript|image/svg\+xml
  • Admin browsing logs (X-Forwarded-For, User-Agent) opening files under /uploads/*.html or /uploads/*.svg shortly before unexpected administrative actions (user creation, role changes, permission modifications)

References

Credits

Reported independently by:

  • @kaminuma (initial report, 2026-01-09)
  • @arkmarta (concurrent report, 2026-01-13 — originally filed as GHSA-r7hp-523c-r8wr, closed as duplicate)

References

@derrickmehaffy derrickmehaffy published to strapi/strapi May 13, 2026
Published to the GitHub Advisory Database May 14, 2026
Reviewed May 14, 2026
Published by the National Vulnerability Database May 14, 2026
Last updated May 15, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(17th percentile)

Weaknesses

Unrestricted Upload of File with Dangerous Type

The product allows the upload or transfer of dangerous file types that are automatically processed within its environment. Learn more on MITRE.

Protection Mechanism Failure

The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. Learn more on MITRE.

CVE ID

CVE-2026-22707

GHSA ID

GHSA-pcw7-5633-82vv

Source code

Credits

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