CVE-2026-33332: Nicegui NiceGUI's Unvalidated Chunk Size Parameter Vulnerability

MODERATE
Advisory Identifier: GHSA-w5g8-5849-vj76
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CVSS 5.3
CWE-20 CWE-770
Published
Advisory Summary

CVE-2026-33332 is a MODERATE (CVSS 5.3) nicegui's unvalidated chunk size parameter vulnerability (CWE-20: Improper Input Validation) affecting Nicegui libraries in the PyPI ecosystem. The issue involves nicegui's unvalidated chunk size parameter in media routes can cause memory exhaustion. Remediation is available by upgrading affected packages to version 3.9.0.

CVE-2026-33332 at a Glance

CVE Identifier CVE-2026-33332
GHSA Identifier GHSA-w5g8-5849-vj76
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-20: Improper Input Validation
Affected Product Nicegui
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-33332

To remediate this vulnerability, upgrade all affected Nicegui dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nicegui fixed: 3.9.0 
pip install nicegui>=3.9.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show nicegui

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-33332, inspect your installed packages using pip:

pip show nicegui

Analyze the terminal output to locate any version of Nicegui in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.9.0), your application is affected.

Note: The pip show nicegui command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Nicegui, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Summary NiceGUI's `app.add_media_file()` and `app.add_media_files()` media routes accept a user-controlled query parameter that influences how files are read during streaming. The parameter is passed to the range-response implementation without validation, allowing an attacker to bypass chunked streaming and force the server to load entire files into memory at once. With large media files and concurrent requests, this can lead to excessive memory consumption, degraded performance, or denial of service. ## Impact **Affected applications:** NiceGUI applications that serve media content via `app.add_media_file()` or `app.add_media_files()`, particularly those serving large files (video, audio). **What an attacker can do:** - Force the server to load entire files into memory instead of streaming them in chunks - Amplify memory usage with concurrent requests to large media files - Cause performance degradation, memory pressure, and potential OOM conditions **Attack difficulty:** Low - requires only a crafted query parameter. ## Remediation Upgrade to a patched version of NiceGUI. As a workaround, restrict access to media endpoints or strip unexpected query parameters at a reverse proxy layer.

CVE-2026-33332 Affected Nicegui Versions

1 component(s)
Fixed Versions:
3.9.0
Product / Package Ecosystem Affected Versions Fixed Version
nicegui
pypi/nicegui
PyPI
< 3.9.0
3.9.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/zauberzeug/nicegui/security/advisories/GHSA-w5g8-5849-vj76
NVD — CVE-2026-33332 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33332
Security Fix Commit FIX COMMIT
https://github.com/zauberzeug/nicegui/commit/9026962b8c4f3f225c98b2fbc35aa6b60cb3495b
Nicegui Source Repository REPOSITORY
https://github.com/zauberzeug/nicegui
Nicegui Release RELEASE
https://github.com/zauberzeug/nicegui/releases/tag/v3.9.0

Frequently Asked Questions

What is CVE-2026-33332?
CVE-2026-33332 is a security vulnerability in Nicegui involving NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion under CWE-20: Improper Input Validation.
Which Nicegui versions are affected?
Affected versions include releases prior to 3.9.0 across affected packages: nicegui.
What version fixes CVE-2026-33332?
Upgrading to 3.9.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nicegui affected?
Yes, nicegui is affected in releases prior to 3.9.0. Upgrade your dependency to 3.9.0 or later.
What is the CVSS score of CVE-2026-33332?
CVE-2026-33332 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-33332?
CVE-2026-33332 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check PyPI dependencies for CVE-2026-33332?
Run the dependency tree command: 'pip show nicegui'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w5g8-5849-vj76",
  "modified" : "2026-03-27T21:57:40Z",
  "published" : "2026-03-19T18:48:27Z",
  "aliases" : [ "CVE-2026-33332" ],
  "summary" : "NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion",
  "details" : "## Summary\n\nNiceGUI's `app.add_media_file()` and `app.add_media_files()` media routes accept a user-controlled query parameter that influences how files are read during streaming. The parameter is passed to the range-response implementation without validation, allowing an attacker to bypass chunked streaming and force the server to load entire files into memory at once.\n\nWith large media files and concurrent requests, this can lead to excessive memory consumption, degraded performance, or denial of service.\n\n## Impact\n\n**Affected applications:** NiceGUI applications that serve media content via `app.add_media_file()` or `app.add_media_files()`, particularly those serving large files (video, audio).\n\n**What an attacker can do:**\n- Force the server to load entire files into memory instead of streaming them in chunks\n- Amplify memory usage with concurrent requests to large media files\n- Cause performance degradation, memory pressure, and potential OOM conditions\n\n**Attack difficulty:** Low - requires only a crafted query parameter.\n\n## Remediation\n\nUpgrade to a patched version of NiceGUI.\n\nAs a workaround, restrict access to media endpoints or strip unexpected query parameters at a reverse proxy layer.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nicegui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
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        "fixed" : "3.9.0"
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    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.8.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
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    "type" : "ADVISORY",
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  }, {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/commit/9026962b8c4f3f225c98b2fbc35aa6b60cb3495b"
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    "type" : "PACKAGE",
    "url" : "https://github.com/zauberzeug/nicegui"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/releases/tag/v3.9.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-19T18:48:27Z",
    "nvd_published_at" : "2026-03-24T20:16:28Z"
  }
}