What is CVE-2021-37705?

CVE-2021-37705 is a critical-severity vulnerability in Microsoft Onefuzz, classified under Improper Authorization. CVSS score: 10.0/10. Published 2021-08-13.

How severe is CVE-2021-37705?

Critical severity. CVSS v3 base score is 10.0 out of 10.

Auth bypass in Microsoft Onefuzz

CVE-2021-37705

OneFuzz is an open source self-hosted Fuzzing-As-A-Service platform. Starting with OneFuzz 2.12.0 or greater, an incomplete authorization check allows an authenticated user from any Azure Active Directory tenant to make authorized API calls to a vulnerable OneFuzz instance. To be vulnerable, a OneFuzz deployment must be both version 2.12.0 or greater and deployed with the non-default --multi_tenant_domain option. This can result in read/write access to private data such as software vulnerability and crash information, security testing tools and proprietary code and symbols. Via authorized API calls, this also enables tampering with existing data and unauthorized code execution on Azure compute resources. This issue is resolved starting in release 2.31.0, via the addition of application-level check of the bearer token's `issuer` against an administrator-configured allowlist. As a workaround users can restrict access to the tenant of a deployed OneFuzz instance < 2.31.0 by redeploying in the default configuration, which omits the `--multi_tenant_domain` option.

Published 2021-08-13 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:L.

EPSS exploit prediction

EPSS: 0.024 (83.5th percentile), scored 2026-10-01.

Low probability of exploitation in the next 30 days, but still tracked. 84th percentile — 83.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.024 · newest: 0.024 · change: 0.000

Affected products

Microsoft Onefuzz — versions >= 2.12.0, < 2.31.0

Weakness classification (CWE)

References

github.com/microsoft/onefuzz/security/advisories/GHSA-q5vh-6whw-x745 (Third Party Advisory)
github.com/microsoft/onefuzz/pull/1153 (Patch, Third Party Advisory)
github.com/microsoft/onefuzz/commit/2fcb4998887959b4fa11894a068d689189742cb1 (Patch, Third Party Advisory)
github.com/microsoft/onefuzz/releases/tag/2.31.0 (Third Party Advisory, Release Notes)
pypi.org/project/onefuzz/ (Product)

Frequently asked questions

What is CVE-2021-37705?: CVE-2021-37705 is a critical-severity vulnerability in Microsoft Onefuzz, classified under Improper Authorization. CVSS score: 10.0/10. Published 2021-08-13.
How severe is CVE-2021-37705?: Critical severity. CVSS v3 base score is 10.0 out of 10.