CVE-2026-27953 | ormar has a Pydantic Validation Bypass via Kwargs Injection in Model Constructor

Exp

ormar is a async mini ORM for Python. Versions 0.23.0 and below are vulnerable to Pydantic validation bypass through the model constructor, allowing any unauthenticated user to skip all field validation by injecting "__pk_only__": true into a JSON request body. By injecting "__pk_only__": true into a JSON request body, an unauthenticated attacker can skip all field validation and persist unvalidated data directly to the database. A secondary __excluded__ parameter injection uses the same pattern to selectively nullify arbitrary model fields (e.g., email or role) during construction. This affects ormar's canonical FastAPI integration pattern recommended in its official documentation, enabling privilege escalation, data integrity violations, and business logic bypass in any application using ormar.Model directly as a request body parameter. This issue has been fixed in version 0.23.1.

Published: 2026-03-19 Last update: 2026-03-27 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-27953 is rated High Exploit Risk (66.4/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.49%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-27953

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-27953

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-26 0.42% 0.49% +0.07%
2 2026-04-21 0.29% 0.42% +0.13%
3 2026-04-20 — 0.29% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-27953

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.1 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 2.8 4.2 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]

Weakness enumeration for CVE-2026-27953

GitHub Security Advisory for CVE-2026-27953

GHSA-f964-whrq-44h8 · Severity: high · Ecosystem: pip — ormar Pydantic Validation Bypass via __pk_only__ and __excluded__ Kwargs Injection in Model Constructor

OS Trackers for CVE-2026-27953

vendor priority summary link
debian not yet assigned CVE-2026-27953 not yet assigned priority: Debian including 1 source packages (ormar), 3 status rows across 3 suites (bookworm, forky, sid): resolved 2, open 1. https://security-tracker.debian.org/tracker/CVE-2026-27953

Affected software / configurations for CVE-2026-27953

Vendor Product Version Raw CPE
collerek ormar < 0.23.1 cpe:2.3:a:collerek:ormar:*:*:*:*:*:python:*:*

References for CVE-2026-27953

URL Tags
https://github.com/ormar-orm/ormar/blob/master/examples/fastapi_quick_start.py#L55 Patch
https://github.com/ormar-orm/ormar/blob/master/ormar/fields/foreign_key.py#L41 Patch
https://github.com/ormar-orm/ormar/blob/master/ormar/models/helpers/pydantic.py#L108 Patch
https://github.com/ormar-orm/ormar/blob/master/ormar/models/model.py#L89 Patch
https://github.com/ormar-orm/ormar/blob/master/ormar/models/newbasemodel.py#L128 Patch
https://github.com/ormar-orm/ormar/blob/master/ormar/models/newbasemodel.py#L292 Patch
https://github.com/ormar-orm/ormar/commit/7f22aa21a7614b993970345b392dabb0ccde0ab3 Patch
https://github.com/ormar-orm/ormar/releases/tag/0.23.1 Product Release Notes
https://github.com/ormar-orm/ormar/security/advisories/GHSA-f964-whrq-44h8 Exploit Mitigation Vendor Advisory
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