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NVD / CVE Program· CNA GitHub_M

CVE-2021-29621: Observable Response Discrepancy in Flask-AppBuilder

MediumCVSS 5.3 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 3.4% (FIRST EPSS); higher than 89% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: dpgaspar Flask-AppBuilder 3.3.0.

Low priority for now. Upgrade to dpgaspar Flask-AppBuilder 3.3.0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Flask-AppBuilder is a development framework, built on top of Flask. User enumeration in database authentication in Flask-AppBuilder <= 3.2.3. Allows for a non authenticated user to enumerate existing accounts by timing the response time from the server when you are logging in. Upgrade to version 3.3.0 or higher to resolve.

Published
Jun 7, 2021
Updated
Jun 16, 2026
EPSS
3.4% · 89th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
21 / 40 · 5.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 3.4%

CNA vs NVD score

NVD
5.3
CNA · GitHub_M
5.3
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-29621

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
dpgasparflask-appbuilder
apacheairflow

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • dpgaspar Flask-AppBuilder

    • < 3.3.0affected

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • apache airflow1.10.0
  • dpgaspar flask-appbuilderup to 3.2.3 inclusive

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
PyPIflask-appbuilderbefore 3.3.03.3.0

Same product

dpgaspar: all records

Other highest-scoring records for the same primary product.

  • CVE-2024-25128Flask-AppBuilder incorrect authentication when using auth type OpenID
    36Monitor
  • CVE-2021-41265Improper Authentication in Flask-AppBuilder
    35Monitor
  • CVE-2023-29005No Rate Limiting on Login AUTH DB
    30Monitor

Published before and after this one in the same product

  • Later →CVE-2021-32805Sep 8, 2021 · URL Redirection to Untrusted Site ('Open Redirect') in Flask-AppBuilder
    24Monitor
  • Later →CVE-2022-21659Jan 31, 2022 · Observable Response Discrepancy in Flask-AppBuilder
    21Monitor
  • Later →CVE-2022-24776Mar 24, 2022 · Open Redirect in Flask-AppBuilder
    24Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
dpgaspar Flask-AppBuilder3.3.0 · descriptionVendor (CNA)
PyPI:flask-appbuilder3.3.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
none
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
None
Availability impact
None

Weakness class (CWE)

CWE-203 · Observable Discrepancy

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records