ormar Pydantic Validation Bypass via __pk_only__ and __excluded__ Kwargs Injection in Model Constructor

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-27953: 1.21% estimated exploitation activity in the next 30 days; percentile 68.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A Pydantic validation bypass in ormar's model constructor allows any unauthenticated user to skip all field validation — type checks, constraints, @fieldvalidator/@modelvalidator decorators, choices enforcement, and required-field checks — by injecting "pkonly": true into a JSON request body. The unvalidated data is subsequently persisted to the database. This affects the canonical usage pattern recommended in ormar's official documentation and examples. A secondary excluded parameter injection uses the same design pattern to selectively nullify arbitrary model fields during construction. Details Root cause: NewBaseModel.init (ormar/models/newbasemodel.py, line 128) pops pkonly directly from user-supplied kwargs before any validation occurs: The pkonly flag was designed as an internal optimization for creating lightweight FK placeholder instances in ormar/fields/foreignkey.py (lines 41, 527). However, because it is extracted from kwargs via .pop() with a False default, any…

Published by the source

19 Mar 2026, 16:27 UTC

Last modified by the source

13 Jul 2026, 07:26 UTC

Source last checked

26 Oct 2026, 13:37 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-f964-whrq-44h8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-f964-whrq-44h8

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# Patch Next advisory brief: CVE-2026-27953

Advisory: ormar Pydantic Validation Bypass via __pk_only__ and __excluded__ Kwargs Injection in Model Constructor
IDs: CVE-2026-27953, GHSA-f964-whrq-44h8
Record: https://patchnext.com/advisories/cve-2026-27953 (revision 2, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ormar 0.23.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI ormar: affected <= 0.23.0; fixed in 0.23.1

## Suggested inspection (read-only)
- `python -m pip show ormar`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ormar.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-f964-whrq-44h8 (OSV record GHSA-f964-whrq-44h8 lists affected ranges: PyPI ormar >=0 <0.23.1 (fixed))
- Verified: https://github.com/advisories/GHSA-f964-whrq-44h8 (GitHub-reviewed advisory GHSA-f964-whrq-44h8 lists affected ranges: PyPI ormar >=0 <=0.23.0)

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