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Medium

Private action arguments can be set by user input in Ash

Type: advisorySources: OSV

Improperly Controlled Modification of Dynamically-Determined Object Attributes vulnerability in ash-project ash allows a user to set the value of a private action argument that is intended to be controlled only by trusted server-side code. Action arguments declared with public?: false are meant to be set internally (for example via Ash.Changeset.set_private_argument/3) and must not be settable from end-user input. When a changeset is built from a parameter map, Ash filters out private arguments, but the filtering is incomplete. In the regular changeset path (for_create, for_update, for_destroy), private arguments are stripped only when the parameter key is an atom. When the key is a binary (string), as is the case for user-supplied parameters, the private argument is kept and the user controls its value. In the atomic path (Ash.Changeset.fully_atomic_changeset/4, also reached through atomic and bulk updates), private arguments are not stripped at all, regardless of whether the key is an atom or a binary. An attacker who can submit parameters to an action that defines a private argument can therefore inject a value for that argument. Depending on how the application uses the argument (for example an acting_user_id driving authorization or record ownership), this can lead to an integrity violation or privilege escalation. This issue affects ash: from 3.0.0 before 3.29.3.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-55736
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 21:24 UTC · Revision 1

Source evidence

Private action arguments can be set by user input in Ash

core-osv · Original source

Published 23 Jun 2026, 18:21 UTC

Improperly Controlled Modification of Dynamically-Determined Object Attributes vulnerability in ash-project ash allows a user to set the value of a private action argument that is intended to be controlled only by trusted server-side code. Action arguments declared with public?: false are meant to be set internally (for example via Ash.Changeset.set_private_argument/3) and must not be settable from end-user input. When a changeset is built from a parameter map, Ash filters out private arguments, but the filtering is incomplete. In the regular changeset path (for_create, for_update, for_destroy), private arguments are stripped only when the parameter key is an atom. When the key is a binary (string), as is the case for user-supplied parameters, the private argument is kept and the user controls its value. In the atomic path (Ash.Changeset.fully_atomic_changeset/4, also reached through atomic and bulk updates), private arguments are not stripped at all, regardless of whether the key is an atom or a binary. An attacker who can submit parameters to an action that defines a private argument can therefore inject a value for that argument. Depending on how the application uses the argument (for example an acting_user_id driving authorization or record ownership), this can lead to an integrity violation or privilege escalation. This issue affects ash: from 3.0.0 before 3.29.3.

osv:CVE-2026-55736
Complete source record
{
  "id": "fde0716b8a4da745eaa2c692d37907a7dac1e5fb2b396c86cf65c0e763060052",
  "url": "https://osv.dev/vulnerability/CVE-2026-55736",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Private action arguments can be set by user input in Ash",
    "summary": "Improperly Controlled Modification of Dynamically-Determined Object Attributes vulnerability in ash-project ash allows a user to set the value of a private action argument that is intended to be controlled only by trusted server-side code. Action arguments declared with public?: false are meant to be set internally (for example via Ash.Changeset.set_private_argument/3) and must not be settable from end-user input. When a changeset is built from a parameter map, Ash filters out private arguments, but the filtering is incomplete. In the regular changeset path (for_create, for_update, for_destroy), private arguments are stripped only when the parameter key is an atom. When the key is a binary (string), as is the case for user-supplied parameters, the private argument is kept and the user controls its value. In the atomic path (Ash.Changeset.fully_atomic_changeset/4, also reached through atomic and bulk updates), private arguments are not stripped at all, regardless of whether the key is an atom or a binary. An attacker who can submit parameters to an action that defines a private argument can therefore inject a value for that argument. Depending on how the application uses the argument (for example an acting_user_id driving authorization or record ownership), this can lead to an integrity violation or privilege escalation. This issue affects ash: from 3.0.0 before 3.29.3.",
    "evidence": "osv:CVE-2026-55736",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-55736",
      "aliases": [
        "CVE-2026-55736",
        "EEF-CVE-2026-55736",
        "GHSA-f4hc-ppw9-4hhw"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
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              "type": "GIT",
              "events": [
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                  "introduced": "0"
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                {
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              "database_specific": {
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                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
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                        "introduced": "3.0.0"
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          }
        }
      ],
      "modified": "2026-10-28T02:30:39.611823954Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-55736.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-55736",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55736.json",
        "https://github.com/ash-project/ash/security/advisories/GHSA-f4hc-ppw9-4hhw",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-55736",
        "https://github.com/ash-project/ash/commit/d9b3100219b3ea86d73202bf7368c03a7688efea",
        "https://github.com/ash-project/ash"
      ],
      "provider_metadata": {
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        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55736.json"
      }
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    "related_cves": [
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        "value": "CVE-2026-55736",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 507232,
  "published_at": "2026-06-23T18:21:13.033+00:00"
}