CVE-2026-53769VulnerabilityPublished 9 Jul 2026

Avo: Direct attachment upload endpoint lacks upload authorization and bypasses field-level upload policy

Affects avoSource GCVE Database

Authoritative record:CVE-2026-53769· Medium 6.5

Not known to be exploited · CVSS 6.5 Medium : upgrade to 3.32.0 when convenient.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 36% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.32.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 4 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: evidence found.
CISA SSVC: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by GitHub, Inc.
10 Jun 202617:48 UTC, 86 days before disclosure
CVE published
on cve.org
4 Sep 202620:02 UTC, t = 0
CISA SSVC assessment
proof of concept public
9 Sep 202615:57 UTC, 5 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA SSVC, the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade avo to 3.32.0.

Affected software

Product	Affected	Fixed in
RubyGemsavo	Affected >=2.28.0 <3.32.0	Fixed in 3.32.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary Avo's direct attachment upload endpoint lacks server-side upload authorization and bypasses the documented field-level upload policy methods such as `upload_{FIELD_ID}?`. An authenticated Avo user who can reach the Avo attachment upload endpoint can replace or add attachment content, including binary content, filename, and content-type metadata, on a resolved record even when both `update?` and `upload_<field>?` policies deny the operation. This primarily affects multi-role Avo Pro/Advanced-style deployments where non-administrator or restricted operator users can reach Avo and per-record or per-field operations are expected to be enforced by policies. ### Details Avo exposes a direct attachment upload endpoint: ```text POST /<avo-root>/avo_api/resources/:resource_name/:id/attachments/ ``` The vulnerable code path is `Avo::AttachmentsController#create`: - `app/controllers/avo/attachments_controller.rb:9-24` Current behavior: ```ruby def create blob = ActiveStorage::Blob.create_and_upload! io: params[:file].to_io, filename: params[:filename] association_name = BaseResource.valid_attachment_name(@record, params[:attachment_key]) if association_name @record.send(association_name).attach blob elsif params[:key].blank? raise ActionController::BadRequest.new(...) end render json: { url: main_app.url_for(blob), href: main_app.url_for(blob) } end ``` This endpoint creates an `ActiveStorage::Blob` before validating the requested attachment association and before any upload authorization could be enforced. If `attachment_key` resolves to an association, the blob is attached to the target record. If the request uses the key-based/Trix path, the endpoint can still persist the blob and return `url`/`href` even when no attachment association is resolved on the target record. The controller never calls: - `@resource.authorization.authorize_action("upload_<field>?", record: @record, ...)` - `@resource.authorization.authorize_action("update?", record: @record, ...)` This is inconsistent with the rest of Avo's file authorization implementation. The field-level file authorization concern defines upload authorization as: - `lib/avo/fields/concerns/file_authorization.rb:11-12` - `lib/avo/fields/concerns/file_authorization.rb:25-27` ```ruby def can_upload_file? authorize_file_action(:upload) end def authorize_file_action(action) authorize_action("#{action}_#{id}?", record: record, raise_exception: false) end ``` That upload policy is used by UI components to decide whether to render upload controls, but the server-side upload endpoint does not enforce the same policy. A user can therefore bypass the policy by directly POSTing to the endpoint. By contrast, attachment deletion does call attachment-specific authorization: - `app/controllers/avo/attachments_controller.rb:27-65` ```ruby def destroy if authorized_to :delete ... end end def authorized_to(action) @resource.authorization.authorize_action("#{action}_#{params[:attachment_name]}?", record: @record, raise_exception: false) end ``` The asymmetry is: - `destroy`: calls `delete_<attachment_name>?` - `create`: does not call `upload_<attachment_key>?` or `update?` The field-level upload authorization intent is also documented by Avo: - Issue #1624 requested the "Ability to police each file upload/download/delete". https://github.com/avo-hq/avo/issues/1624 - PR #1625 introduced `upload_cover_photo?` as an example upload policy method. https://github.com/avo-hq/avo/pull/1625 - PR #1667 clarified the policy semantics: "From now on, only field level authorization will be considered. If it is defined and returns true, the action will be granted; otherwise, it will not." https://github.com/avo-hq/avo/pull/1667 - The current Avo authorization documentation lists `upload_{FIELD_ID}?` as the policy method controlling whether a user can upload an attachment, stating: "Controls whether the user can upload the attachment." https://docs.avohq.io/4.0/authorization.html - The same documentation says the same `upload_file?` policy method will be used to "authorize the file upload" in action file fields. https://docs.avohq.io/4.0/authorization.html Affected versions observed: - PoC-confirmed: Avo `3.31.2`, commit `46aa6b3bc9e3283110c39e58cfec8bb95adc1897` - Same vulnerable code path by source inspection: `origin/main` HEAD as of 2026-05-29, `9e23ddc88f2b1e762e4a5ec35a6f86370ac16c73` - Same vulnerable code path by source inspection: Avo `v4.0.0.beta.26`, `6d339595a27f8779cb99b4aa38ddc97cb702b30f` - Same vulnerable code path by source inspection: `origin/4-dev` at version `4.0.0.beta.40`, `7ab9794f8b044b11b9677cdc57547d99cf96c3f3` Suggested affected range for the GitHub Security Advisory form: ```text >= 2.28.0 ``` Rationale: - The direct attachment upload endpoint exists without upload authorization from commit `ab5f5970e2aa76e6ca0a95bf04f510ba7ed5e858` (`feature: trix atta

CWE-862Missing Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #4OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
Attack patterns
Exploitation of Thunderbolt Protection Flaws (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-863Incorrect Authorization (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #17OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
Architecture and Design
Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
Architecture and Design
Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

Loading reviews…

Exploitation evidence

Timeline

What to do

Affected software

Description

WeaknessesCWE-862, CWE-863

Technical details

References

Community reviews

Related threats